sederhanakan! a. sin 52 sin 68 - sin 47 cos 77 cos 65 cos 81 b. sin 45 cos 15 + cos 45 sin 15 tolong kasih tau caranya. jangan pelit

a.sin 52 sin 68-sin47 cos77-cos65 cos81
=-1/2(cos(52-68)-cos(52-68))-1/2 sin(47+77)+sin47-77))
-1/2(cos(65+81)+cos(65-81).
=-1/2 cos120+1/2cos(-16)-1/2 sin124-1/2 sin(-30)-1/2cos146-1/2 cos(-16)
=-1/2(-1/2)+1/2 cos 16-1/2 sin 124-1/2(-1/2)-1/2 cos146-1/2 cos 16
=1/4-1/2 sin 124+1/4-1/2 cos 146
=1/2-1/2 sin 124-1/2 cos 146
=1/2-1/2sin 124-1/2(-sin56)
=1/2-1/2 sin124+1/2sin56
=1/2-1/2(sin124-sin56)
=1/2-1/2(2cos1/2(124+56)sin1/2(124-56)
=1/2-1/2(2cos 90 sin 34)
=1/2-(0)(sin 34)=1/2.

b.sin 45 cos 15+cos 45 sin 15
=ada rumus
sin a cos b+ cos a sin b=sin(a+b)
maka berlaku:
sin 45 cos 15+cos45 sin 15=sin(45+15)
sin 45 cos 15+cos 45 sin 15=sin 60
sin 45 cos 15+cos 45 sin 15=1 per 2 akar 3.