Jika tan x = 1,2 tentukan nilai dari sin (3/2 pi + x) + cos (x - 2 pi) = ?

Persamaan trigonometri

tan x = 1,2 = 12/10= 6/5 = y/x
r = √x²+y² = √25+36 = √61
cos x = x/r= 5/√61


sin (3/2 π + x ) + cos (x - 2π) =
= sin (3/2 π + x ) + cos {-(2π - x)}
=  sin (3/2 π + x)  + cos (2π -x)
=  - cos x -  cos x
= - 2 cos x
= - 2 (5)/(√61)
= -10/61  √61