cos(a+b) = cos(b) cos(a)-sin(a) sin(b)
tan^{ 2 }(x)+1=sec^{ 2 }(x)
cos(a+b)=cos(b)cos(a)-sin(a)sin(b)
sin(a-b) = sin(a) cos(b)-cos(a) sin(b)
sin(a+b) = sin(a) cos(b)+cos(a) sin(b)
sin^{ 2 }x+{ cos }^{ 2 }x=1
cot^{ 2 }(x)+1=csc^{ 2 }(x)
