y^2+5y the greatest common factor is y so
y(y+5)
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4x^2-49 this is a "difference of perfect squares" which always factors to:
(a^2-b^2)=(a-b)(a+b), in this case:
(2x-7)(2x+7)
...
5s^2-20 GCF is 5
5(s^2-4) now the parenthetic term is a difference of squares so
5(s-2)(s+2)
