The difference of squares pattern tells us that (a+b)(a-b)=a²-b². This can be used to expand (x+2)(x-2) as x²-4, but also to expand (3+5x⁴)(3-5x⁴) as 9-25x⁸, or (3y²+2y⁵)(3y²-2y⁵) as 9y⁴-4y¹⁰.
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