jika 1 - cot a = ⅓, maka sin 2a + cos 2a?

1 - 1/tan(a) = 1/3
1/tan(a) = 1 - 1/3 = 2/3
tan(a) = 3/2
sin(a) = 3/akar(3^2+2^2) = 3/akar(13) =3/akar(13)
cos(a) = 2/akar(3^2+2^2) = 2/akar(13) =2/akar(13) 

sin 2a + cos 2a
= 2 sin a cos a + cos^2 a - sin^2 a
= 2 . 3/akar(13) . 2/akar(13) + (2/akar(13))^2 - (3/akar(13))^2
= 12/13 + 4/13 - 9/13
= ...... itung sndiri