Find the zeros of the following quadratic polynomials and verify the relationship between the zeros and the coefficients:
Question:
Find the zeros of the following quadratic polynomials and verify the relationship between the zeros and the coefficients:
$2 x^{2}-x-6$
Solution:
Let $f(x)=2 x^{2}-x-6$
To find the zeroes, we put $f(x)=0$
$\Rightarrow 2 x^{2}-x-6=0$
$\Rightarrow 2 x^{2}-4 x+3 x-6=0$
$\Rightarrow 2 x(x-2)+3(x-2)=0$
$\Rightarrow(x-2)(2 x+3)=0$
$\Rightarrow(x-2)=0$ or $(2 x+3)=0$
$\Rightarrow x=2,-\frac{3}{2}$
Hence, all the zeroes of the polynomial $f(x)$ are 2 and $-\frac{3}{2}$.
Now,
$f(2)=2(2)^{2}-2-6$
$=2(4)-8$
$=8-8$
$=0$
$f\left(-\frac{3}{2}\right)=2\left(-\frac{3}{2}\right)^{2}-\left(-\frac{3}{2}\right)-6$
$=2\left(\frac{9}{4}\right)+\frac{3}{2}-6$
$=\frac{9}{2}+\frac{3}{2}-6$
$=\frac{12}{2}-6$
$=6-6$
$=0$
Hence, the relationship between the zeros and the coefficients is verified.