How do you factor $3y^2 -21y+36$ ?

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Answer 1 · 2015-08-11T16:56:05

$color(green)((3y-9)(y-4)$ is the factorised form of the expression.

$3y^2−21y+36$

We can Split the Middle Term of this expression to factorise it.

In this technique, if we have to factorise an expression like $ay^2 + by + c$ , we need to think of two numbers such that:

$N_1*N_2 = a*c = 3*36 = 108$

and,

$N_1 +N_2 = b = -21$

After trying out a few numbers we get $N_1 = -12$ and $N_2 =-9$

$(-12)*(-9) = 108$ , and $(-12)+(-9)= -21$

$3y^2−color(green)(21y)+36 = 3y^2color(green)(-12y-9y)+36$

$=3y(y-4) -9(y-4)$

$color(green)((3y-9)(y-4)$ is the factorised form of the expression.

How do you factor 3y^2 -21y+363y^2 -21y+36?