Question

упростите (cos a +sin a) в квадрате-2sin a cos a

Answer 1

(cos a    =  sin a)^2  -  2sin a cos a  =  sin^2 a  -  2sin a cos a  +  cos^2 a  +  
+  2sin a cos a  =  sin^2 a  +  cos^2 a  =  1

Answer 2

(Cosa+sina)^2-2sinacosa= cos^2a+2cosasina+sin^2a-2sinacosa=cos^2a+sin^2a=1