document.write( "Question 285481: cos^4[x]-sin^4[x]=cos^2[x]-sin^2[x]
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Algebra.Com's Answer #207201 by toidayma(44)\"\" \"About 
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Since a^2 - b^2 = (a-b)(a+b), apply this with a = cos^2(x) and b = sin^2(x). You have:
\n" ); document.write( "\"cos%5E4%28x%29+-+sin%5E4%28x%29\" = \"%28cos%5E2%28x%29+-+sin%5E2%28x%29%29%28cos%5E2%28x%29+%2B+sin%5E2%28x%29%29\"
\n" ); document.write( "Since with every x, sin^2(x) + cos^2(x) = 1, therefore, you can scratch out the factor (cos^2(x) + sin^2(x)). So, cos^4(x) - sin^4(x) = cos^2(x) - sin^2(x).
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