Practicing Success
If $4 cos θ + 3 sin θ = x$ and $4 sin θ − 3 cos θ = y$, find the value of $x^ 2 + y^2$. |
16 9 25 1 |
25 |
4 cos θ + 3 sin θ = x and 4 sin θ − 3 cos θ = y On squaring both the equations and adding , ( 4 cos θ + 3 sin θ)² +( 4 sin θ − 3 cos θ )² = x² + y² 16 cos² θ + 9 sin² θ + 24 cos θ . sin θ + 16 sin² θ + 9 cos² θ . 24 cos θ . sin θ = x² + y² 16 cos² θ + 9 sin² θ + 16 sin² θ + 9 cos² θ = x² + y² { using sin² θ + cos² θ = 1 } 16 ( cos² θ + sin² θ) + 9 ( sin² θ + cos² θ) = x² + y² x² + y² = 16 + 9 x² + y² = 25 |