Is it possible to factor $y=x^2+x-12$ ? If so, what are the factors?

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Answer 1 · 2016-07-07T18:33:43

$y=(x-3)(x+4).$

Yes, $y=f(x), say, = x^2+x-12$ can be factorised into two linear factors.

In fact, a quadratic polynomial like $ax^2+bx+c$ can be factorised [ in RR], if and only if, $Delta=b^2-4ac>=0.$

In our case, we are having, $a=1, b= 1, c=-12,$ so, $Delta=1-4*1*(-12)=1+48=49>=0$ , hence, given $f$ can be factorised.

Its factors are $(x-alpha), (x-beta)$ , where, $alpha=( -b+sqrtDelta)/(2a)=(-1+sqrt49)/(2*1)=(-1+7)/2=3$

and, #beta=(-b-sqrtDelta0/(2a)=(-1-7)/2=-8/2=-4.

Hence the factors are $(x-3) and, (x+4).$

$:. y=(x-3)(x+4).$

Another Method, is, as follows :-

$y=f(x), say, = x^2+x-12$
$:. y=x^2+4x-3x-12.....................[4xx3=12, 4-3=1]$
$=x(x+4)-3(x+4)=(x+4)(x-3)$ , as before!

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Answer 2 · 2016-07-07T19:06:20

$(x + 4)(x-3)$

Find two factors of 12 which differ (because of the MINUS 12) by 1, as indicated by the coefficient of the x term.

With a basic knowledge of the times tables we find:

$4xx3 = 12 " and " +4 - 3 = +1$
These then are the factors we need. The MINUS 12 also indicates that the sign will be different, (neg x pos = neg)

$(x + 4)(x-3)$

Is it possible to factor y=x^2+x-12 y=x^2+x-12 ? If so, what are the factors?