Question

if cos 9 alpha is equal to sin alpha and 9alpha less than 90degrees

Answer 1

Alpha is 9 and 9alpha is 81.
The solution is
Cosθ=Sin(90-θ)
Cos9alpha=son alpha
But cos 9alpha=son(90-9alpha)

Therefore
Alpha =90-9alpha
Thus
10alpha=90
So
Alpha =90/10
Alpha =9
And 9alpha =81





Hope it helps