Have you tried rewriting the original function as
?
∫(from 0 to pi/2) 7^cost sint dt
i know that it is a^u du
but sin needs to be negative so I tried this:
-∫(from 0 to pi/2) 7^cost (-sint) dt
then made u=cost and du= -sint
so: ∫ 7^u du= 7^u/ ln7= 7^cost /ln7
and when i plug in pi/2 i get 1/ln7
but the answer is 6/ln7