How do you factor $5y^2-90$ ?

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Answer 1 · 2016-04-18T06:44:18

$5y^2-90 = 5(y-3sqrt(2))(y+3sqrt(2))$

Separate out the common scalar factor $5$ , express as a difference of squares, then use the difference of squares identity:

$a^2-b^2=(a-b)(a+b)$

with $a=y$ and $b=3sqrt(2)$ as follows:

$5y^2-90$

$= 5(y^2-18)$

$= 5(y^2-3^2*2)$

$= 5(y^2-(3sqrt(2))^2)$

$= 5(y-3sqrt(2))(y+3sqrt(2))$

How do you factor 5y^2-905y^2-90?