Can i know the steps to these questions?

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

formula: sin^2 + cos^2 = 1

2.
tan a tan(90-a) + sin^2 + cos^2
= tan a tan(90-a) + 1
= tan a / tan a + 1 = 2

formula: sin^2 + cos^2 = 1
tan(90-a) = 1/tan(a)