Trig Help Please?

Question

please explain, i don't understand how to do it:

1. Find the exact value of the trigonmetric function [cos(x+y)]given that sinx = 3/5 and cosy = - 5/13 in quadrant 2.

2.Find the exact value of the sine, cosine, and tangent of 285 degrees.

Answer 1

cos (x+y) = cos x cos y - sin x sin y

to find cos x given sin x, remember that sin^2 x + cos^2 x = 1

part deux:

285 = 225 + 60. exact values of 225 (5 pi / 4) and 60 (pi / 3) are known. use the sum formulas to get sin and cos. Divide sin/cos to get tan

Answer 2

Question 1
cos(x + y) = cos x.cos y - sin x.siny
cos(x + y) = (- 4/5).(- 5/13) - (3/5).(12/13)
cos(x + y) = 20 / 65 - 36 / 65
cos(x + y) = - 16 / 65
Question 2
sin 285°
= sin (360 - 75)°
= sin 360°.cos 75° - cos 360°.sin 75°
= - sin 75°
= - sin (45 + 30)°
= - [ sin 45°.cos 30° + cos 45°.sin 30°]
= - [ (1/√2).(√3/2) + (1/√2).(1/2) ]
= - (1 / (2√2)).[ √3 + 1 ]
Will leave cos and tan to you----too much typing involved!
What do you mean,"lazy ******!!!!"