How do you factor $y^2-17y+72$ ?

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Answer 1 · 2017-02-13T00:17:15

$y^2-17y+72 = (y-8)(y-9)$

Note that:

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

So if we can find factors $a, b$ of $72$ with sum $17$ then we can find a factorisation.

Note that:

$8*9 = 72" "$ and $" "8+9 = 17$

So:

$y^2-17y+72 = (y-8)(y-9)$

How do you factor y^2-17y+72y^2-17y+72?