Question

Need help with this question quick. Pre calculus question

Answer 1

Answer: -56/65

sin α = 4/5 => cos α = 3/5 (because 0 < α < pi/2)

cos β = -12/13 ⇒ sin β = 5/13 (because pi/2 < β < pi)

we have:

cos(α + β) = cosα.cosβ - sinα.sinβ =
`(3)/(5).(-12)/(13)-(4)/(5).(5)/(13)=(-56)/(65)`

Explanation: