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.
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
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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.