Trig Expression 05303D
1. The problem states: Given that $x + y = 90^\circ$, find the value of the expression
$$\frac{\cos(2x + y) + \sin(3x + 2y)}{\cos y}$$
2. First, use the given relation $x + y = 90^\circ$ to express angles in terms of one variable. Since $y = 90^\circ - x$, substitute this into the expression.
3. Substitute $y = 90^\circ - x$:
$$\cos(2x + y) = \cos(2x + 90^\circ - x) = \cos(x + 90^\circ)$$
$$\sin(3x + 2y) = \sin(3x + 2(90^\circ - x)) = \sin(3x + 180^\circ - 2x) = \sin(x + 180^\circ)$$
4. Use trigonometric identities:
- $\cos(\theta + 90^\circ) = -\sin \theta$
- $\sin(\theta + 180^\circ) = -\sin \theta$
So,
$$\cos(x + 90^\circ) = -\sin x$$
$$\sin(x + 180^\circ) = -\sin x$$
5. Substitute back:
$$\frac{\cos(2x + y) + \sin(3x + 2y)}{\cos y} = \frac{-\sin x + (-\sin x)}{\cos y} = \frac{-2 \sin x}{\cos y}$$
6. Recall $y = 90^\circ - x$, so $\cos y = \cos(90^\circ - x) = \sin x$.
7. Substitute $\cos y = \sin x$:
$$\frac{-2 \sin x}{\sin x} = -2$$
8. Therefore, the value of the expression is $-2$.
Final answer: A) $-2$