In each of the following, find the value of k for which the given value is a solution of the given equation:
In each of the following, find the value of k for which the given value is a solution of the given equation:
(i) $7 x^{2}+k x-3=0, x=\frac{2}{3}$
(ii) $x^{2}-x(a+b)+k=0, x=a$
(iii) $k x^{2}+\sqrt{2} x-4=0, x=\sqrt{2}$
(iv) $x^{2}+3 a x+k=0, x=-a$
In each of the following cases find k.
(i) We are given here that,
$7 x^{2}+k x-3=0, x=\frac{2}{3}$
Now, as we know that $x=\frac{2}{3}$ is a solution of the quadratic equation, hence it should satisfy the equation. Therefore substituting $x=\frac{2}{3}$ in the above equation gives us,
$7\left(\frac{2}{3}\right)^{2}+k\left(\frac{2}{3}\right)-3=0$
$\frac{28+6 k-27}{3}=0$
$6 k=-1$
$k=-\frac{1}{6}$
Hence, the value of $k=-\frac{1}{6}$.
(ii) We are given here that,
$x^{2}-x(a+b)+k=0, x=a$
Now, as we know that is a solution of the quadratic equation, hence it should satisfy the equation. Therefore substituting in the above equation gives us,
$a^{2}-a(a+b)+k=0$
$a^{2}-a^{2}-a b+k=0$
$k=a b$
Hence, the value of $k=a b$.
(iii) We are given here that,
$k x^{2}-\sqrt{2} x-4=0, x=\sqrt{2}$
Now, as we know that $x=\sqrt{2}$ is a solution of the quadratic equation, hence it should satisfy the equation. Therefore substituting $x=\sqrt{2}$ in the above equation gives us,
$k(\sqrt{2})^{2}+\sqrt{2}(\sqrt{2})-4=0$
$2 k+2-4=0$
$2 k=2$
$k=1$
Hence, the value of $k=1$.
(iv) We are given here that,
$x^{2}+3 a x+k=0, x=-a$
Now, as we know that $x=-a$ is a solution of the quadratic equation, hence it should satisfy the equation. Therefore substituting $x=-a$ in the above equation gives us,
$(-a)^{2}+3 a(-a)+k=0$
$a^{2}-3 a^{2}+k=0$
$k=2 a^{2}$
Hence the value of $k=2 a^{2}$.