Find the number of pairs (x, y) satisfying the equations sin x + sin y...
Understanding the Equations
To solve the equations sin x + sin y = sin (x + y) and |x| + |y| = 1, we start with the trigonometric identity.
Trigonometric Identity Analysis
The equation sin x + sin y = sin (x + y) can be rewritten using the sum-to-product identities:
- sin x + sin y = 2 sin((x + y)/2) cos((x - y)/2)
- sin (x + y) = sin x cos y + cos x sin y
This shows that the equation simplifies to 0, leading to the conditions:
- (x + y) = nπ or (x - y) = nπ for some integer n.
Exploring the Absolute Value Condition
The second equation, |x| + |y| = 1, indicates that we are restricted to the boundaries of a diamond shape in the xy-plane. The vertices of this diamond are (1, 0), (0, 1), (-1, 0), and (0, -1).
Finding Solutions
Now, we need to find pairs (x, y) that satisfy both conditions:
1. First Quadrant:
- (1, 0)
- (0, 1)
2. Second Quadrant:
- (-1, 0)
- (0, 1)
3. Third Quadrant:
- (-1, 0)
- (0, -1)
4. Fourth Quadrant:
- (1, 0)
- (0, -1)
Counting Unique Solutions
- Each pair (x, y) satisfying the absolute value condition gives us solutions where x and y can be interchanged, leading to additional valid pairs.
- The combinations yield the pairs: (1, 0), (0, 1), (-1, 0), (0, -1), and their negative counterparts.
Final Count
This analysis leads to a total of 6 unique pairs satisfying both equations:
- (1, 0)
- (0, 1)
- (-1, 0)
- (0, -1)
- (0.5, 0.5)
- (-0.5, -0.5)
Thus, the answer is 6.