How sin(90+x) become -coos(x). What about the 90. Explain.
Actually, I got that wrong. Sorry. But the addition formula says
sin(90+x) = sin90 cosx + cos90 sinx = sinx
consider that sin(100) = sin(90+10) = sin(180-100) = sin(80) = cos(10)
sin(90+x) = sin90 cosx + cos90 sinx = sinx
consider that sin(100) = sin(90+10) = sin(180-100) = sin(80) = cos(10)