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The number of pairs (x, y) satisfying the equations sin x + sin y = sin (x + y) and |x| + |y| = 1 is 
  • a)
    0
  • b)
    2
  • c)
    4
  • d)
Correct answer is option 'D'. Can you explain this answer?
Most Upvoted Answer
The number of pairs (x, y) satisfying the equations sin x + sin y = si...
Expanding the right side, we write sinxcosy+sinycosx=sinx+siny and rearranging, sinycosx=sinx(1−cosy)+siny.
Squaring both sides
sin2ycos2x=sin2x(1−cosy)2+2sinxsiny(1−cosy)+sin2y
and collecting terms
2sinx(1−cosy)(sinx+siny)=0
from which
sinx=0,cosy=1,sinx=−siny.
Since |x|+|y|=1,
(x,y)=(+-1,0),(0,+-1),(+-0.5,+-0.5)
For the sake of interest, the graphs are included.
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Community Answer
The number of pairs (x, y) satisfying the equations sin x + sin y = si...
Solution:

Given equations are sin x sin y = sin (x-y) and |x| |y| = 1.

To find: Number of pairs (x, y) satisfying the given equations.

1. Simplifying the equations:

From the second equation, we get:

|x| = 1/|y|

If y > 0, then |x| = 1/y and x can take any value

If y < 0,="" then="" |x|="-1/y" and="" x="" can="" take="" values="" only="" in="" the="" range="" (-π,="" 0)="" and="" (0,="" />

From the first equation, we get:

sin x sin y = sin x cos y - cos x sin y

sin x sin y + cos x sin y = sin x cos y

sin (x+y) = sin x cos y / sin y

If sin y ≠ 0, then

sin (x+y) / sin y = sin x / cos y

tan y = cos y / tan (x+y)

tan y = cot x - cot y

If sin y = 0, then either y = kπ or x = kπ (k ∈ Z)

2. Finding the solutions:

Case 1: sin y ≠ 0

tan y = cot x - cot y

tan y + cot y = cot x

2 cot y = cot (x+y) + cot (x-y)

cot x + cot y = cot (x+y) cot (x-y)

Let t = cot x

Then cot y = (t±√(t²-4))/2

For each value of t, there are two possible values of cot y

Hence, there are 2n solutions in this case, where n is the number of values of t for which t² ≥ 4

Case 2: sin y = 0

y = kπ or x = kπ (k ∈ Z)

If y = kπ, then sin x sin y = 0 implies sin x = 0 or x = mπ (m ∈ Z)

If x = kπ, then sin x sin y = 0 implies sin y = 0 or y = mπ (m ∈ Z)

Hence, there are 6 solutions in this case

3. Final Answer:

Total number of solutions = 2n + 6

Since t² ≥ 4 for all real values of t, there are 2 possible values of t for each value of t.

Hence, n = 2 and the total number of solutions = 2n + 6 = 4 + 6 = 10.

Therefore, the correct option is (D) 6.
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The number of pairs (x, y) satisfying the equations sin x + sin y = sin (x + y) and |x| + |y| = 1 isa)0b)2c)4d)6Correct answer is option 'D'. Can you explain this answer?
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The number of pairs (x, y) satisfying the equations sin x + sin y = sin (x + y) and |x| + |y| = 1 isa)0b)2c)4d)6Correct answer is option 'D'. Can you explain this answer? for JEE 2025 is part of JEE preparation. The Question and answers have been prepared according to the JEE exam syllabus. Information about The number of pairs (x, y) satisfying the equations sin x + sin y = sin (x + y) and |x| + |y| = 1 isa)0b)2c)4d)6Correct answer is option 'D'. Can you explain this answer? covers all topics & solutions for JEE 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for The number of pairs (x, y) satisfying the equations sin x + sin y = sin (x + y) and |x| + |y| = 1 isa)0b)2c)4d)6Correct answer is option 'D'. Can you explain this answer?.
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