1. Cos^2 x=1-sin^x
Cos^x=1-9/25
cos^2 x=25-9/25
cos^2 x=16/25
cos x=+- 4/5 dar x apartine de la 0 la pi/2 deci cosx=4/5
2. 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 dar y apartine de la 0 la pi/2 dexi cos y=12/13
cos(x+y)=cosxcoy-sinxsiny
cos(x+y)=4/5•12/13-3/5•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 adv
ptr ca sin^2 x+cos^2 x=1
^- la patrat
/-supra
