Dear Student,

aCosA = 1

This implies Cos A = 1/a......................................................................(Equation1)

bSinA = 1

This implies Sin A = 1/b .........................................................................(Equation 2)

Tan A  = Sin A/Cos A..............................................................................(Equation 3)

Therefore ,

From (1),(2) &  (3)

we get,

Tan A = (1/b)/(1/a)

TanA = a/b