Question

Is it -56/65????????????????

Answer 1

Answer:

$\cos (u + v) = -\dfrac{56}{65}$

Good job!

Step-by-step explanation:

$\cos (u + v) = \cos u \cos v - \sin u \sin v$

$\sin u = -\dfrac{3}{5}$; u is in QIII.

That makes $\cos u = -\dfrac{4}{5}$

$\sin v = -\dfrac{12}{13}$; v is in QIV.

That makes $\cos v = \dfrac{5}{13}$

$\cos (u + v) = (-\dfrac{4}{5})(\dfrac{5}{13}) - (-\dfrac{3}{5})(-\dfrac{12}{13})$

$\cos (u + v) = -\dfrac{20}{65} - \dfrac{36}{65}$

$\cos (u + v) = -\dfrac{56}{65}$

You are correct.

Answer 2

Answer:

Step-by-step explanation:

-0.8615