tan^2x - sin^2x = sin^2x • tan^2x

Question

I don’t know how to figure out this proof. the only relationship i can think of is tan = sin/cos 

Answer 1

Work with the left hand side (LHS):

=sin²x(1/cos²x - 1)  = sin²x(1-cos²x)/cos²x = sin²x•sin²x / cos²x= sin²x•tan²x  = RHS.

Q.E.D.