How do you factor #4x^2+15x+9#?

1 Answer
George C.
Jun 22, 2016

#4x^2+15x+9=(4x+3)(x+3)#

Explanation:

Use an AC method.

Find a pair of factors of #AC = 4*9 = 36# with sum #B=15#

The pair #12, 3# works in that #12+3 = 15# and #12xx3=36#

Use this pair to split the middle term, then factor by grouping...

#4x^2+15x+9#

#=4x^2+12x+3x+9#

#=(4x^2+12x)+(3x+9)#

#=4x(x+3)+3(x+3)#

#=(4x+3)(x+3)#

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