Question

Mă puteți ajuta va rog?​

Answer 1

1. sin^2 x+cos^2 x =1
9/25+cos^2 x=1
Cos^2 x=1-9/25
cos^2 x=25-9/25
cos^2 x= 16/25
cos ^ 2 x= + - 4/5
x apartine de la 0 la pi/2 deci cos x =4/5

2. Cos(x+y)=cosxcosy-sinxsiny
cos^2 y= 1-sin^2 y
cos^2 y= 1-25/169
Cos^2 y=169-25/169
cos^2 y=144/169
cos y=+ - 12/13
Y apartine la 0,pi/2 deci cos y=12/13
cos(x+y)= 12/13•4/5-3/5•5/13
Cos(x+y)= 48/65-15/65
cos(x+y)=33/65

3. (Sinx +cosx)^2 +(sinx-cosx)^2=2
sin^2 x +cos^2 x +2sinxcosx +sin^2 x +cos^2 x -2sinxcosx=2
1+1=2
2=2