Question

is secA*cosA =1 for all A where 0<=A<=90? please provide a solution

Answer 1

Trick question

(1/cos A)(cos A) = 1
unless cos A = 0
but what is cos 90 ?

If A = 90. in fact the secant is just plain not defined.
http://socratic.org/questions/what-is-the-exact-value-of-sec-90