Question

Limit as x approaches pi/2 from the negative for sec(3x)cos(7x)

Answer 1

I would look at a graph, and find the answer. then I would use epsilon delta proof to prove it. I do not know of an elementary way to answer this. Normally I would say plug in pi/2 - .0000000000000001, but since this something with an oscillating amplitude, things tend to get funky around any "problem areas".

Answer 2

so you could get some very different numbers for pi/2 - 10^(-10) vs pi/2 - 10^(-11)

Answer 3

Have you learnt l'hopital's rule yet?