Question

докажите тождество
1) (sina+cosa)^2+(sina-cosa)^2=2
2) sin^4a-sin^2a=cos^4a-cos^2a
3) ctg^2a-cos^2a=ctg^2a*cos^2a

Answer 1

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