Question 444926
We have {{{64x^2 - 100y^2}}}
Notice that we have a difference of squares and recall the formula for the difference of squares:  {{{(a^2 -b^2) = (a+b)(a-b)}}}. 

Also notice that {{{64x^2 = (8x)^2}}} and {{{100y^2 = (10y)^2}}} This is why they are perfect squares.
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So following the formula {{{64x^2-100y^2 = (8x)^2 - (10y)^2 = (8x+10y)(8x-10y)}}}

Notice that a "2" is common in each factor, so we can factor out a 2.
{{{2(4x+5y) * 2(4x-5y)}}}. Now collect 2*2 to get 4 and we have our answer.
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{{{4*(4x+5y)*(4x-5y)}}}
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If you'd like, FOIL this out to check.