Answer:
cosx = sqrt(15)/4, -sqrt(15)/4
Step-by-step explanation:
cos²x = 1 - sin²sin x
cos²x = 1 - (1/4)²
cos²x = 15/16
1+1 = 2
3*4=12
12-2=10
10*2=20
20+15=35
35*2=70
