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Page 1 13. Complex Numbers Exercise 13.1 1. Question Evaluate the following: (i) i 457 (ii) i 528 (iii) (iv) (v) (vi) (i 77 + i 70 + i 87 + i 414 ) 3 (vii) (vii) i 30 + i 40 + i 60 (viii) i 49 + i 68 + i 89 + i 118 Answer i. i 457 = i (456 + 1) = i 4(114) × i = (1) 114 × i = i since i 4 = 1 ii. i 528 = i 4(132) = (1) 132 =1 since i 4 = 1 iii. since i 4 = 1 = – 1 since i 2 = – 1 iv. [since i 4 = 1] v. = (i – i) = 0 [since ] Page 2 13. Complex Numbers Exercise 13.1 1. Question Evaluate the following: (i) i 457 (ii) i 528 (iii) (iv) (v) (vi) (i 77 + i 70 + i 87 + i 414 ) 3 (vii) (vii) i 30 + i 40 + i 60 (viii) i 49 + i 68 + i 89 + i 118 Answer i. i 457 = i (456 + 1) = i 4(114) × i = (1) 114 × i = i since i 4 = 1 ii. i 528 = i 4(132) = (1) 132 =1 since i 4 = 1 iii. since i 4 = 1 = – 1 since i 2 = – 1 iv. [since i 4 = 1] v. = (i – i) = 0 [since ] vi. (i 77 + i 70 + i 87 + i 414 ) 3 = (i (76 + 1) + i (68 + 2) + i (84 + 3) + i (412 + 2) ) 3 (i 77 + i 70 + i 87 + i 414 ) 3 = (i + i 2 + i 3 + i 2 ) 3 [since i 3 = – i, i 2 = – 1] = (i + (– 1) + (– i) + (– 1)) 3 = (– 2) 3 (i 77 + i 70 + i 87 + i 414 ) 3 = –8 vii. i 30 + i 40 + i 60 = i (28 + 2) + i 40 + i 60 = (i 4 ) 7 i 2 + (i 4 ) 10 + (i 4 ) 15 = i 2 + 1 10 + 1 15 = – 1 + 1 + 1 = 1 viii. i 49 + i 68 + i 89 + i 118 = i (48 + 1) + i 68 + i (88 + 1) + i (116 + 2) = (i 4 ) 12 ×i + (i 4 ) 17 + (i 4 ) 11 ×i + (i 4 ) 29 ×i 2 = i + 1 + i – 1 = 2i 2. Question Show that 1 + i 10 + i 20 + i 30 is a real number ? Answer 1 + i 10 + i 20 + i 30 = 1 + i (8 + 2) + i 20 + i (28 + 2) = 1 + (i 4 ) 2 × i 2 + (i 4 ) 5 + (i 4 ) 7 × i 2 = 1 – 1 + 1 – 1 = 0 [ since i 4 = 1, i 2 = – 1] Hence , 1 + i 10 + i 20 + i 30 is a real number. 3 A. Question Find the value of following expression: i 49 + i 68 + i 89 + i 110 Answer i 49 + i 68 + i 89 + i 110 = i (48 + 1) + i 68 + i (88 + 1) + i (108 + 2) = (i 4 ) 12 × i + (i 4 ) 17 + (i 4 ) 11 × i + (i 4 ) 27 × i 2 = i + 1 + i – 1 = 2i [since i 4 = 1, i 2 = – 1] i 49 + i 68 + i 89 + i 110 = 2i 3 B. Question Find the value of following expression: i 30 + i 80 + i 120 Answer i 30 + i 80 + i 120 = i (28 + 2) + i 80 + i 120 = (i 4 ) 7 × i 2 + (i 4 ) 20 + (i 4 ) 30 = – 1 + 1 + 1 = 1 Page 3 13. Complex Numbers Exercise 13.1 1. Question Evaluate the following: (i) i 457 (ii) i 528 (iii) (iv) (v) (vi) (i 77 + i 70 + i 87 + i 414 ) 3 (vii) (vii) i 30 + i 40 + i 60 (viii) i 49 + i 68 + i 89 + i 118 Answer i. i 457 = i (456 + 1) = i 4(114) × i = (1) 114 × i = i since i 4 = 1 ii. i 528 = i 4(132) = (1) 132 =1 since i 4 = 1 iii. since i 4 = 1 = – 1 since i 2 = – 1 iv. [since i 4 = 1] v. = (i – i) = 0 [since ] vi. (i 77 + i 70 + i 87 + i 414 ) 3 = (i (76 + 1) + i (68 + 2) + i (84 + 3) + i (412 + 2) ) 3 (i 77 + i 70 + i 87 + i 414 ) 3 = (i + i 2 + i 3 + i 2 ) 3 [since i 3 = – i, i 2 = – 1] = (i + (– 1) + (– i) + (– 1)) 3 = (– 2) 3 (i 77 + i 70 + i 87 + i 414 ) 3 = –8 vii. i 30 + i 40 + i 60 = i (28 + 2) + i 40 + i 60 = (i 4 ) 7 i 2 + (i 4 ) 10 + (i 4 ) 15 = i 2 + 1 10 + 1 15 = – 1 + 1 + 1 = 1 viii. i 49 + i 68 + i 89 + i 118 = i (48 + 1) + i 68 + i (88 + 1) + i (116 + 2) = (i 4 ) 12 ×i + (i 4 ) 17 + (i 4 ) 11 ×i + (i 4 ) 29 ×i 2 = i + 1 + i – 1 = 2i 2. Question Show that 1 + i 10 + i 20 + i 30 is a real number ? Answer 1 + i 10 + i 20 + i 30 = 1 + i (8 + 2) + i 20 + i (28 + 2) = 1 + (i 4 ) 2 × i 2 + (i 4 ) 5 + (i 4 ) 7 × i 2 = 1 – 1 + 1 – 1 = 0 [ since i 4 = 1, i 2 = – 1] Hence , 1 + i 10 + i 20 + i 30 is a real number. 3 A. Question Find the value of following expression: i 49 + i 68 + i 89 + i 110 Answer i 49 + i 68 + i 89 + i 110 = i (48 + 1) + i 68 + i (88 + 1) + i (108 + 2) = (i 4 ) 12 × i + (i 4 ) 17 + (i 4 ) 11 × i + (i 4 ) 27 × i 2 = i + 1 + i – 1 = 2i [since i 4 = 1, i 2 = – 1] i 49 + i 68 + i 89 + i 110 = 2i 3 B. Question Find the value of following expression: i 30 + i 80 + i 120 Answer i 30 + i 80 + i 120 = i (28 + 2) + i 80 + i 120 = (i 4 ) 7 × i 2 + (i 4 ) 20 + (i 4 ) 30 = – 1 + 1 + 1 = 1 [since i 4 = 1, i 2 = – 1] i 30 + i 80 + i 120 = 1 3 C. Question Find the value of following expression: i + i 2 + i 3 + i 4 Answer i + i 2 + i 3 + i 4 = i + i 2 + i 2 ×i + i 4 = i – 1 + (– 1)×i + 1 since i 4 = 1, i 2 = – 1 = i – 1 – i + 1 = 0 3 D. Question Find the value of following expression: i 5 + i 10 + i 15 Answer i 5 + i 10 + i 15 = i (4 + 1) + i (8 + 2) + i (12 + 3) = (i 4 ) 1 ×i + (i 4 ) 2 ×i 2 + (i 4 ) 3 ×i 3 = (i 4 ) 1 ×i + (i 4 ) 2 ×i 2 + (i 4 ) 3 ×i 2 ×i = 1×i + 1×(– 1) + 1×(– 1)×i = i – 1 – i = – 1 3 E. Question Find the value of following expression: Answer = i 10 = i 8 i 2 = (i 4 ) 2 i 2 Since i 4 = 1, i 2 = -1 = (1) 2 (-1) = -1 3 F. Question Find the value of following expression: 1 + i 2 + i 4 + i 6 + i 8 + ... + i 20 Answer 1 + i 2 + i 4 + i 6 + i 8 + ... + i 20 = 1 + (– 1) + 1 + (– 1) + 1 + ... + 1 = 1 3 G. Question Find the value of following expression: (1 + i) 6 + (1 – i) 3 Page 4 13. Complex Numbers Exercise 13.1 1. Question Evaluate the following: (i) i 457 (ii) i 528 (iii) (iv) (v) (vi) (i 77 + i 70 + i 87 + i 414 ) 3 (vii) (vii) i 30 + i 40 + i 60 (viii) i 49 + i 68 + i 89 + i 118 Answer i. i 457 = i (456 + 1) = i 4(114) × i = (1) 114 × i = i since i 4 = 1 ii. i 528 = i 4(132) = (1) 132 =1 since i 4 = 1 iii. since i 4 = 1 = – 1 since i 2 = – 1 iv. [since i 4 = 1] v. = (i – i) = 0 [since ] vi. (i 77 + i 70 + i 87 + i 414 ) 3 = (i (76 + 1) + i (68 + 2) + i (84 + 3) + i (412 + 2) ) 3 (i 77 + i 70 + i 87 + i 414 ) 3 = (i + i 2 + i 3 + i 2 ) 3 [since i 3 = – i, i 2 = – 1] = (i + (– 1) + (– i) + (– 1)) 3 = (– 2) 3 (i 77 + i 70 + i 87 + i 414 ) 3 = –8 vii. i 30 + i 40 + i 60 = i (28 + 2) + i 40 + i 60 = (i 4 ) 7 i 2 + (i 4 ) 10 + (i 4 ) 15 = i 2 + 1 10 + 1 15 = – 1 + 1 + 1 = 1 viii. i 49 + i 68 + i 89 + i 118 = i (48 + 1) + i 68 + i (88 + 1) + i (116 + 2) = (i 4 ) 12 ×i + (i 4 ) 17 + (i 4 ) 11 ×i + (i 4 ) 29 ×i 2 = i + 1 + i – 1 = 2i 2. Question Show that 1 + i 10 + i 20 + i 30 is a real number ? Answer 1 + i 10 + i 20 + i 30 = 1 + i (8 + 2) + i 20 + i (28 + 2) = 1 + (i 4 ) 2 × i 2 + (i 4 ) 5 + (i 4 ) 7 × i 2 = 1 – 1 + 1 – 1 = 0 [ since i 4 = 1, i 2 = – 1] Hence , 1 + i 10 + i 20 + i 30 is a real number. 3 A. Question Find the value of following expression: i 49 + i 68 + i 89 + i 110 Answer i 49 + i 68 + i 89 + i 110 = i (48 + 1) + i 68 + i (88 + 1) + i (108 + 2) = (i 4 ) 12 × i + (i 4 ) 17 + (i 4 ) 11 × i + (i 4 ) 27 × i 2 = i + 1 + i – 1 = 2i [since i 4 = 1, i 2 = – 1] i 49 + i 68 + i 89 + i 110 = 2i 3 B. Question Find the value of following expression: i 30 + i 80 + i 120 Answer i 30 + i 80 + i 120 = i (28 + 2) + i 80 + i 120 = (i 4 ) 7 × i 2 + (i 4 ) 20 + (i 4 ) 30 = – 1 + 1 + 1 = 1 [since i 4 = 1, i 2 = – 1] i 30 + i 80 + i 120 = 1 3 C. Question Find the value of following expression: i + i 2 + i 3 + i 4 Answer i + i 2 + i 3 + i 4 = i + i 2 + i 2 ×i + i 4 = i – 1 + (– 1)×i + 1 since i 4 = 1, i 2 = – 1 = i – 1 – i + 1 = 0 3 D. Question Find the value of following expression: i 5 + i 10 + i 15 Answer i 5 + i 10 + i 15 = i (4 + 1) + i (8 + 2) + i (12 + 3) = (i 4 ) 1 ×i + (i 4 ) 2 ×i 2 + (i 4 ) 3 ×i 3 = (i 4 ) 1 ×i + (i 4 ) 2 ×i 2 + (i 4 ) 3 ×i 2 ×i = 1×i + 1×(– 1) + 1×(– 1)×i = i – 1 – i = – 1 3 E. Question Find the value of following expression: Answer = i 10 = i 8 i 2 = (i 4 ) 2 i 2 Since i 4 = 1, i 2 = -1 = (1) 2 (-1) = -1 3 F. Question Find the value of following expression: 1 + i 2 + i 4 + i 6 + i 8 + ... + i 20 Answer 1 + i 2 + i 4 + i 6 + i 8 + ... + i 20 = 1 + (– 1) + 1 + (– 1) + 1 + ... + 1 = 1 3 G. Question Find the value of following expression: (1 + i) 6 + (1 – i) 3 Answer (1 + i) 6 + (1 – i) 3 = {(1 + i) 2 } 3 + (1 – i) 2 (1 – i) = {1 + i 2 + 2i} 3 + (1 + i 2 – 2i)(1 – i) = {1 – 1 + 2i} 3 + (1 – 1 – 2i)(1 – i) = (2i) 3 + (– 2i)(1 – i) = 8i 3 + (– 2i) + 2i 2 [since i 3 = – i, i 2 = – 1] = – 8i – 2i – 2 = – 10 i – 2 = – 2(1 + 5i) Exercise 13.2 1 A. Question Express the following complex numbers in the standard form a + i b : (1 + i) (1 + 2i) Answer Given: ? a+ib = (1+i)(1+2i) ? a+ib = 1(1+2i)+i(1+2i) ? a+ib = 1+2i+i+2i 2 We know that i 2 =-1 ? a+ib = 1+3i+2(-1) ? a+ib = 1+3i-2 ? a+ib=-1+3i ? The values of a, b are -1, 3. 1 B. Question Express the following complex numbers in the standard form a + i b : Answer Given: ? Multiplying and dividing with -2-i ? ? We know that i 2 =-1 Page 5 13. Complex Numbers Exercise 13.1 1. Question Evaluate the following: (i) i 457 (ii) i 528 (iii) (iv) (v) (vi) (i 77 + i 70 + i 87 + i 414 ) 3 (vii) (vii) i 30 + i 40 + i 60 (viii) i 49 + i 68 + i 89 + i 118 Answer i. i 457 = i (456 + 1) = i 4(114) × i = (1) 114 × i = i since i 4 = 1 ii. i 528 = i 4(132) = (1) 132 =1 since i 4 = 1 iii. since i 4 = 1 = – 1 since i 2 = – 1 iv. [since i 4 = 1] v. = (i – i) = 0 [since ] vi. (i 77 + i 70 + i 87 + i 414 ) 3 = (i (76 + 1) + i (68 + 2) + i (84 + 3) + i (412 + 2) ) 3 (i 77 + i 70 + i 87 + i 414 ) 3 = (i + i 2 + i 3 + i 2 ) 3 [since i 3 = – i, i 2 = – 1] = (i + (– 1) + (– i) + (– 1)) 3 = (– 2) 3 (i 77 + i 70 + i 87 + i 414 ) 3 = –8 vii. i 30 + i 40 + i 60 = i (28 + 2) + i 40 + i 60 = (i 4 ) 7 i 2 + (i 4 ) 10 + (i 4 ) 15 = i 2 + 1 10 + 1 15 = – 1 + 1 + 1 = 1 viii. i 49 + i 68 + i 89 + i 118 = i (48 + 1) + i 68 + i (88 + 1) + i (116 + 2) = (i 4 ) 12 ×i + (i 4 ) 17 + (i 4 ) 11 ×i + (i 4 ) 29 ×i 2 = i + 1 + i – 1 = 2i 2. Question Show that 1 + i 10 + i 20 + i 30 is a real number ? Answer 1 + i 10 + i 20 + i 30 = 1 + i (8 + 2) + i 20 + i (28 + 2) = 1 + (i 4 ) 2 × i 2 + (i 4 ) 5 + (i 4 ) 7 × i 2 = 1 – 1 + 1 – 1 = 0 [ since i 4 = 1, i 2 = – 1] Hence , 1 + i 10 + i 20 + i 30 is a real number. 3 A. Question Find the value of following expression: i 49 + i 68 + i 89 + i 110 Answer i 49 + i 68 + i 89 + i 110 = i (48 + 1) + i 68 + i (88 + 1) + i (108 + 2) = (i 4 ) 12 × i + (i 4 ) 17 + (i 4 ) 11 × i + (i 4 ) 27 × i 2 = i + 1 + i – 1 = 2i [since i 4 = 1, i 2 = – 1] i 49 + i 68 + i 89 + i 110 = 2i 3 B. Question Find the value of following expression: i 30 + i 80 + i 120 Answer i 30 + i 80 + i 120 = i (28 + 2) + i 80 + i 120 = (i 4 ) 7 × i 2 + (i 4 ) 20 + (i 4 ) 30 = – 1 + 1 + 1 = 1 [since i 4 = 1, i 2 = – 1] i 30 + i 80 + i 120 = 1 3 C. Question Find the value of following expression: i + i 2 + i 3 + i 4 Answer i + i 2 + i 3 + i 4 = i + i 2 + i 2 ×i + i 4 = i – 1 + (– 1)×i + 1 since i 4 = 1, i 2 = – 1 = i – 1 – i + 1 = 0 3 D. Question Find the value of following expression: i 5 + i 10 + i 15 Answer i 5 + i 10 + i 15 = i (4 + 1) + i (8 + 2) + i (12 + 3) = (i 4 ) 1 ×i + (i 4 ) 2 ×i 2 + (i 4 ) 3 ×i 3 = (i 4 ) 1 ×i + (i 4 ) 2 ×i 2 + (i 4 ) 3 ×i 2 ×i = 1×i + 1×(– 1) + 1×(– 1)×i = i – 1 – i = – 1 3 E. Question Find the value of following expression: Answer = i 10 = i 8 i 2 = (i 4 ) 2 i 2 Since i 4 = 1, i 2 = -1 = (1) 2 (-1) = -1 3 F. Question Find the value of following expression: 1 + i 2 + i 4 + i 6 + i 8 + ... + i 20 Answer 1 + i 2 + i 4 + i 6 + i 8 + ... + i 20 = 1 + (– 1) + 1 + (– 1) + 1 + ... + 1 = 1 3 G. Question Find the value of following expression: (1 + i) 6 + (1 – i) 3 Answer (1 + i) 6 + (1 – i) 3 = {(1 + i) 2 } 3 + (1 – i) 2 (1 – i) = {1 + i 2 + 2i} 3 + (1 + i 2 – 2i)(1 – i) = {1 – 1 + 2i} 3 + (1 – 1 – 2i)(1 – i) = (2i) 3 + (– 2i)(1 – i) = 8i 3 + (– 2i) + 2i 2 [since i 3 = – i, i 2 = – 1] = – 8i – 2i – 2 = – 10 i – 2 = – 2(1 + 5i) Exercise 13.2 1 A. Question Express the following complex numbers in the standard form a + i b : (1 + i) (1 + 2i) Answer Given: ? a+ib = (1+i)(1+2i) ? a+ib = 1(1+2i)+i(1+2i) ? a+ib = 1+2i+i+2i 2 We know that i 2 =-1 ? a+ib = 1+3i+2(-1) ? a+ib = 1+3i-2 ? a+ib=-1+3i ? The values of a, b are -1, 3. 1 B. Question Express the following complex numbers in the standard form a + i b : Answer Given: ? Multiplying and dividing with -2-i ? ? We know that i 2 =-1 ? ? ? ? The values of a, b are . 1 C. Question Express the following complex numbers in the standard form a + i b : Answer Given: ? ? We know that i 2 =-1 ? ? Multiplying and diving with 3-4i ? ? ? ? ? ? The values of a, b is . 1 D. Question Express the following complex numbers in the standard form a + i b : Answer Given: ? Multiplying and dividing by 1-iRead More
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