Question

Which two values of x are roots of the polynomial below?
x2-11x + 15

Answer 1

The two values of roots of the polynomial $x^{2}-11 x+15$ are $\frac{11+\sqrt{61}}{2} \text { or } \frac{11-\sqrt{61}}{2}$

Solution:

Given, polynomial expression is $x^{2}-11 x+15$

We have to find the roots of the given expression.

In order to find roots, now let us use quadratic formula.

$x=\frac{-b \pm \sqrt{b^{2}-4 a c}}{2 a}$

Given that $x^{2}-11 x+15$

Here a = 1, b = -11 and c = 15

On substituting the values we get,

$x=\frac{-(-11) \pm \sqrt{(-11)^{2}-4 \times 1 \times 15}}{2 \times 1}$

$\begin{array}{l}{x=\frac{11 \pm \sqrt{121-60}}{2}} \\\\ {x=\frac{11 \pm \sqrt{61}}{2}} \\\\ {x=\frac{11+\sqrt{61}}{2} \text { or } \frac{11-\sqrt{61}}{2}}\end{array}$

Hence, the roots of given polynomial are $\frac{11+\sqrt{61}}{2} \text { or } \frac{11-\sqrt{61}}{2}$