How do you factor $x^2-2x-80$ ?

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Answer 1 · 2016-03-10T15:57:32

$color(blue)( (x + 8 ) (x -10)$ is the factorised form of the expression.

$x^2 -2x -80$

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

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

$N_1*N_2 = a*c = 1*(-80) = -80$

AND

$N_1 +N_2 = b = -2$

After trying out a few numbers we get $N_1 = -10$ and $N_2 =8$
$8*(-10) = -80$ , and $8+(-10)= -2$

$x^2 -2x -80 =x^2 -10x +8x -80$

$= x(x -10) +8 (x -10)$

$=color(blue)( (x + 8 ) (x -10)$

How do you factor x^2-2x-80x^2-2x-80?