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)#