SOLUTION: Hi i have to solve this problem, thanks for help. Sin^4x - Cos^4x = Sin^2x

SOLUTION: Hi i have to solve this problem, thanks for help. Sin^4x - Cos^4x = Sin^2x - Cos^2x

Question 1042158: Hi i have to solve this problem, thanks for help.
Sin^4x - Cos^4x = Sin^2x - Cos^2x
Answer by ikleyn(52798) (Show Source): You can put this solution on YOUR website!
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Hi i have to solve this problem, thanks for help.
Sin^4x - Cos^4x = Sin^2x - Cos^2x
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Are you familiar with this identity:  = {a+b)*(a-b)?


If not, or if you are not sure, look into the lesson The difference of squares formula in this site.



OK. Now, apply this identity to the left side. You will get


 = .

But the first parentheses,   is equal to 1, as everybody knows.

Therefore, 

 = .

QED.

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