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Page 1 5. Trigonometric Functions Exercise 5.1 1. Question Prove the following identities sec 4 x – sec 2 x = tan 4 x + tan 2 x Answer LHS = sec 4 x – sec 2 x = (sec 2 x) 2 – sec 2 x We know sec 2 ? = 1 + tan 2 ?. = (1 + tan 2 x) 2 – (1 + tan 2 x) = 1 + 2tan 2 x + tan 4 x – 1 - tan 2 x = tan 4 x + tan 2 x = RHS Hence proved. 2. Question Prove the following identities sin 6 x + cos 6 x = 1 – 3 sin 2 x cos 2 x Answer LHS = sin 6 x + cos 6 x = (sin 2 x) 3 + (cos 2 x) 3 We know that a 3 + b 3 = (a + b) (a 2 + b 2 – ab) = (sin 2 x + cos 2 x) [(sin 2 x) 2 + (cos 2 x) 2 – sin 2 x cos 2 x] We know that sin 2 x + cos 2 x = 1 and a 2 + b 2 = (a + b) 2 – 2ab = 1 × [(sin 2 x + cos 2 x) 2 – 2sin 2 x cos 2 x – sin 2 x cos 2 x = 1 2 - 3sin 2 x cos 2 x = 1 - 3sin 2 x cos 2 x = RHS Hence proved. 3. Question Prove the following identities (cosecx – sinx) (secx – cosx) (tanx + cotx) = 1 Answer LHS = (cosecx – sinx) (secx – cosx) (tanx + cotx) We know that Page 2 5. Trigonometric Functions Exercise 5.1 1. Question Prove the following identities sec 4 x – sec 2 x = tan 4 x + tan 2 x Answer LHS = sec 4 x – sec 2 x = (sec 2 x) 2 – sec 2 x We know sec 2 ? = 1 + tan 2 ?. = (1 + tan 2 x) 2 – (1 + tan 2 x) = 1 + 2tan 2 x + tan 4 x – 1 - tan 2 x = tan 4 x + tan 2 x = RHS Hence proved. 2. Question Prove the following identities sin 6 x + cos 6 x = 1 – 3 sin 2 x cos 2 x Answer LHS = sin 6 x + cos 6 x = (sin 2 x) 3 + (cos 2 x) 3 We know that a 3 + b 3 = (a + b) (a 2 + b 2 – ab) = (sin 2 x + cos 2 x) [(sin 2 x) 2 + (cos 2 x) 2 – sin 2 x cos 2 x] We know that sin 2 x + cos 2 x = 1 and a 2 + b 2 = (a + b) 2 – 2ab = 1 × [(sin 2 x + cos 2 x) 2 – 2sin 2 x cos 2 x – sin 2 x cos 2 x = 1 2 - 3sin 2 x cos 2 x = 1 - 3sin 2 x cos 2 x = RHS Hence proved. 3. Question Prove the following identities (cosecx – sinx) (secx – cosx) (tanx + cotx) = 1 Answer LHS = (cosecx – sinx) (secx – cosx) (tanx + cotx) We know that We know that sin 2 x + cos 2 x = 1. = 1 = RHS Hence proved. 4. Question Prove the following identities cosecx (secx – 1) – cotx (1 – cosx) = tanx – sinx Answer LHS = cosecx (secx – 1) – cotx (1 – cosx) We know that We know that 1 – cos 2 x = sin 2 x. = RHS Hence proved. 5. Question Prove the following identities Answer LHS We know that Page 3 5. Trigonometric Functions Exercise 5.1 1. Question Prove the following identities sec 4 x – sec 2 x = tan 4 x + tan 2 x Answer LHS = sec 4 x – sec 2 x = (sec 2 x) 2 – sec 2 x We know sec 2 ? = 1 + tan 2 ?. = (1 + tan 2 x) 2 – (1 + tan 2 x) = 1 + 2tan 2 x + tan 4 x – 1 - tan 2 x = tan 4 x + tan 2 x = RHS Hence proved. 2. Question Prove the following identities sin 6 x + cos 6 x = 1 – 3 sin 2 x cos 2 x Answer LHS = sin 6 x + cos 6 x = (sin 2 x) 3 + (cos 2 x) 3 We know that a 3 + b 3 = (a + b) (a 2 + b 2 – ab) = (sin 2 x + cos 2 x) [(sin 2 x) 2 + (cos 2 x) 2 – sin 2 x cos 2 x] We know that sin 2 x + cos 2 x = 1 and a 2 + b 2 = (a + b) 2 – 2ab = 1 × [(sin 2 x + cos 2 x) 2 – 2sin 2 x cos 2 x – sin 2 x cos 2 x = 1 2 - 3sin 2 x cos 2 x = 1 - 3sin 2 x cos 2 x = RHS Hence proved. 3. Question Prove the following identities (cosecx – sinx) (secx – cosx) (tanx + cotx) = 1 Answer LHS = (cosecx – sinx) (secx – cosx) (tanx + cotx) We know that We know that sin 2 x + cos 2 x = 1. = 1 = RHS Hence proved. 4. Question Prove the following identities cosecx (secx – 1) – cotx (1 – cosx) = tanx – sinx Answer LHS = cosecx (secx – 1) – cotx (1 – cosx) We know that We know that 1 – cos 2 x = sin 2 x. = RHS Hence proved. 5. Question Prove the following identities Answer LHS We know that We know that a 3 + b 3 = (a + b) (a 2 + b 2 – ab) We know that sin 2 x + cos 2 x = 1. = sinx = RHS Hence proved. 6. Question Prove the following identities = (secx cosecx + 1) Answer LHS We know that We know that a 3 - b 3 = (a - b) (a 2 + b 2 + ab) We know that sin 2 x + cos 2 x = 1. Page 4 5. Trigonometric Functions Exercise 5.1 1. Question Prove the following identities sec 4 x – sec 2 x = tan 4 x + tan 2 x Answer LHS = sec 4 x – sec 2 x = (sec 2 x) 2 – sec 2 x We know sec 2 ? = 1 + tan 2 ?. = (1 + tan 2 x) 2 – (1 + tan 2 x) = 1 + 2tan 2 x + tan 4 x – 1 - tan 2 x = tan 4 x + tan 2 x = RHS Hence proved. 2. Question Prove the following identities sin 6 x + cos 6 x = 1 – 3 sin 2 x cos 2 x Answer LHS = sin 6 x + cos 6 x = (sin 2 x) 3 + (cos 2 x) 3 We know that a 3 + b 3 = (a + b) (a 2 + b 2 – ab) = (sin 2 x + cos 2 x) [(sin 2 x) 2 + (cos 2 x) 2 – sin 2 x cos 2 x] We know that sin 2 x + cos 2 x = 1 and a 2 + b 2 = (a + b) 2 – 2ab = 1 × [(sin 2 x + cos 2 x) 2 – 2sin 2 x cos 2 x – sin 2 x cos 2 x = 1 2 - 3sin 2 x cos 2 x = 1 - 3sin 2 x cos 2 x = RHS Hence proved. 3. Question Prove the following identities (cosecx – sinx) (secx – cosx) (tanx + cotx) = 1 Answer LHS = (cosecx – sinx) (secx – cosx) (tanx + cotx) We know that We know that sin 2 x + cos 2 x = 1. = 1 = RHS Hence proved. 4. Question Prove the following identities cosecx (secx – 1) – cotx (1 – cosx) = tanx – sinx Answer LHS = cosecx (secx – 1) – cotx (1 – cosx) We know that We know that 1 – cos 2 x = sin 2 x. = RHS Hence proved. 5. Question Prove the following identities Answer LHS We know that We know that a 3 + b 3 = (a + b) (a 2 + b 2 – ab) We know that sin 2 x + cos 2 x = 1. = sinx = RHS Hence proved. 6. Question Prove the following identities = (secx cosecx + 1) Answer LHS We know that We know that a 3 - b 3 = (a - b) (a 2 + b 2 + ab) We know that sin 2 x + cos 2 x = 1. We know that = cosecx × secx + 1 = secx cosecx + 1 = RHS Hence proved. 7. Question Prove the following identities Answer LHS We know that a 3 ± b 3 = (a ± b) (a 2 + b 2 ± ab) We know that sin 2 x + cos 2 x = 1. = 1 - sinx cosx + 1 + sinx cosx = 2 = RHS Hence proved. 8. Question Prove the following identities (secx sec y + tanx tan y) 2 – (secx tan y + tanx sec y) 2 = 1 Answer LHS = (secx sec y + tanx tan y) 2 – (secx tan y + tanx sec y) 2 = [(secx sec y) 2 + (tanx tan y) 2 + 2 (secx sec y) (tanx tan y)] – [(secx tan y) 2 + (tanx sec y) 2 + 2 (secx tan y) (tanx sec y)] = [sec 2 x sec 2 y + tan 2 x tan 2 y + 2 (secx sec y) (tanx tan y)] – [sec 2 x tan 2 y + tan 2 x sec 2 y + 2 (sec 2 x tan 2 y) (tanx sec y)] = sec 2 x sec 2 y - sec 2 x tan 2 y + tan 2 x tan 2 y - tan 2 x sec 2 y = sec 2 x (sec 2 y - tan 2 y) + tan 2 x (tan 2 y - sec 2 y) = sec 2 x (sec 2 y - tan 2 y) - tan 2 x (sec 2 y - tan 2 y) We know that sec 2 x – tan 2 x = 1. = sec 2 x × 1 – tan 2 x × 1 = sec 2 x – tan 2 x = 1 Page 5 5. Trigonometric Functions Exercise 5.1 1. Question Prove the following identities sec 4 x – sec 2 x = tan 4 x + tan 2 x Answer LHS = sec 4 x – sec 2 x = (sec 2 x) 2 – sec 2 x We know sec 2 ? = 1 + tan 2 ?. = (1 + tan 2 x) 2 – (1 + tan 2 x) = 1 + 2tan 2 x + tan 4 x – 1 - tan 2 x = tan 4 x + tan 2 x = RHS Hence proved. 2. Question Prove the following identities sin 6 x + cos 6 x = 1 – 3 sin 2 x cos 2 x Answer LHS = sin 6 x + cos 6 x = (sin 2 x) 3 + (cos 2 x) 3 We know that a 3 + b 3 = (a + b) (a 2 + b 2 – ab) = (sin 2 x + cos 2 x) [(sin 2 x) 2 + (cos 2 x) 2 – sin 2 x cos 2 x] We know that sin 2 x + cos 2 x = 1 and a 2 + b 2 = (a + b) 2 – 2ab = 1 × [(sin 2 x + cos 2 x) 2 – 2sin 2 x cos 2 x – sin 2 x cos 2 x = 1 2 - 3sin 2 x cos 2 x = 1 - 3sin 2 x cos 2 x = RHS Hence proved. 3. Question Prove the following identities (cosecx – sinx) (secx – cosx) (tanx + cotx) = 1 Answer LHS = (cosecx – sinx) (secx – cosx) (tanx + cotx) We know that We know that sin 2 x + cos 2 x = 1. = 1 = RHS Hence proved. 4. Question Prove the following identities cosecx (secx – 1) – cotx (1 – cosx) = tanx – sinx Answer LHS = cosecx (secx – 1) – cotx (1 – cosx) We know that We know that 1 – cos 2 x = sin 2 x. = RHS Hence proved. 5. Question Prove the following identities Answer LHS We know that We know that a 3 + b 3 = (a + b) (a 2 + b 2 – ab) We know that sin 2 x + cos 2 x = 1. = sinx = RHS Hence proved. 6. Question Prove the following identities = (secx cosecx + 1) Answer LHS We know that We know that a 3 - b 3 = (a - b) (a 2 + b 2 + ab) We know that sin 2 x + cos 2 x = 1. We know that = cosecx × secx + 1 = secx cosecx + 1 = RHS Hence proved. 7. Question Prove the following identities Answer LHS We know that a 3 ± b 3 = (a ± b) (a 2 + b 2 ± ab) We know that sin 2 x + cos 2 x = 1. = 1 - sinx cosx + 1 + sinx cosx = 2 = RHS Hence proved. 8. Question Prove the following identities (secx sec y + tanx tan y) 2 – (secx tan y + tanx sec y) 2 = 1 Answer LHS = (secx sec y + tanx tan y) 2 – (secx tan y + tanx sec y) 2 = [(secx sec y) 2 + (tanx tan y) 2 + 2 (secx sec y) (tanx tan y)] – [(secx tan y) 2 + (tanx sec y) 2 + 2 (secx tan y) (tanx sec y)] = [sec 2 x sec 2 y + tan 2 x tan 2 y + 2 (secx sec y) (tanx tan y)] – [sec 2 x tan 2 y + tan 2 x sec 2 y + 2 (sec 2 x tan 2 y) (tanx sec y)] = sec 2 x sec 2 y - sec 2 x tan 2 y + tan 2 x tan 2 y - tan 2 x sec 2 y = sec 2 x (sec 2 y - tan 2 y) + tan 2 x (tan 2 y - sec 2 y) = sec 2 x (sec 2 y - tan 2 y) - tan 2 x (sec 2 y - tan 2 y) We know that sec 2 x – tan 2 x = 1. = sec 2 x × 1 – tan 2 x × 1 = sec 2 x – tan 2 x = 1 = RHS Hence proved. 9. Question Prove the following identities Answer RHS We know that sin 2 x + cos 2 x = 1. We know that 1 – cos 2 x = sin 2 x. We know that 1 – sin 2 x = cos 2 x.Read More
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