# How do you find the exact value of sin(u+v) given that sinu=-7/25 and cosv=-4/5?

Feb 28, 2017

Question undefined

#### Explanation:

Use trig identity:
sin (u + v) = sin u.cos v + sin v.cos u
We know: $\sin u = - \frac{7}{25}$ and $\cos v = - \frac{4}{5}$. Find cos u and sin v.
${\cos}^{2} u = 1 - {\sin}^{2} u = 1 - \frac{49}{625} = \frac{576}{625}$ --> $\cos u = \pm \frac{24}{25}$
We can't determine cos u because we don't know which Quadrant angle u is in.
The same problem with sin v.