SOLUTION: Assume that sin x= 0.8 and sin y= square root of 0.75. find cos (x+y)

Algebra ->  Trigonometry-basics -> SOLUTION: Assume that sin x= 0.8 and sin y= square root of 0.75. find cos (x+y)      Log On


   

Question 665365: Assume that sin x= 0.8 and sin y= square root of 0.75. find cos (x+y)
Answer by lwsshak3(11628) About Me  (Show Source):
You can put this solution on YOUR website!
Assume that sin x= 0.8 and sin y= square root of 0.75. find cos (x+y)
**
Identity: cos(x+y)=cosxcosy-sinxsiny
..
sinx=0.8=8/10=4/5 (3-4-5 right triangle)
cosx=3/5
siny=√.75=√3/4=√3/2
y=π/3
cosy=1/2
..
cos(x+y)=cosxcosy-sinxsiny
=3/5*1/2-4/5*√3/2
=3/10-4√3/10
=(3-4√3)/10