How am I suppose to transform the left side of the equation into the right side using trig identities? ):

Question

1) sin^2θ - cos^2θ = 2 sin^2θ - 1

Answer 1

sin^2x + cos^2x = 1
from the above,we make cos^2x the subject of the formula:
cos^2x = 1- sin^2x......................(1)
substituting the above into the left hand side of original equation:

sin^2x - ( 1 - sin^2x )
expanding the bracket and noting that - times - equals +
sin^2x - 1 + sin^2x
rearranging:
2sin^2x - 1.