tolong di bantu yaah

cos β = 3/5 .... sin β = 4/5
sin α = - ⅔... cos α = -√5/3
tg α = 2√5 /5
tg β = 4/3

a) = sin α cos β + cos α sin β
= (-⅔) ³/5 + (-√5/3) 4/5
= (-6 - 4√5) / 15
= - (6 + 4√5) / 15

b) = cos α cos β + sin α sin β
= (-√5/3) ³/5 + (-⅔) 4/5
= (-3√5-8) /15
= - (3√5 + 8) / 15

c) = (tg α - tg β) / (1 + tg α tg β)
= (2√5/5 - 4/3)/ (1 + 2√5/5. 4/3)
= (6√5-20) / (15 + 8√5)
= (6√5-20)(15-8√5) / (15²- (8√5)²)
= 90√5-240-300+160√5 / (225-320)
= 250√5 - 540 / -95
= 540+250√5 / 95
= (108 + 50√5) / 19