Question 310834
Prove the identity:

{{{2Cos^2x -1 = Cos^2x -Sin^2x}}}
{{{2Cos^2x -1 = Cos^2x -(1-Cos^2x)}}}
{{{2Cos^2x -1 = Cos^2x -1+Cos^2x}}}
{{{2Cos^2x -1 = 2Cos^2x -1}}}