Question

Find the value of the following expression, when x = -1:
$2{x^2} - x - 2$

Answer 1

Hint – This problem is based upon the concept of simple substitution, simply substitute the value of x as -1 in the expression $2{x^2} - x - 2$. Simplify to get the answer.

Complete step-by-step answer:
Given expression is
$2{x^2} - x - 2$
Now we have to find the value of this expression at x = -1.
So substitute x = -1 in the given expression we have,
$ \Rightarrow 2{\left( { - 1} \right)^2} - \left( { - 1} \right) - 2$
Now simplify the above equation we have,
As we know $(-1)^2$ is positive and (1) and – (-1) = 1 so use this in above equation we have,
$ \Rightarrow 2\left( 1 \right) + 1 - 2$
$ \Rightarrow 2 + 1 - 2 = 1$
So this is the required answer.

Note – The given equation $2{x^2} - x - 2$ is a quadratic equation. Any quadratic equation can be expressed in the form of $a{x^2} + bx + c = 0{\text{ where a}} \ne {\text{0}}$. The simplification of this quadratic equation could have been done in another way, if we would have first factorized the given equation in terms of its roots and then substituted the value of x then also the answer would have been. But it was not done because it would have only lengthened the simplification process.