The values of $k$ for which the equation $4 x^{2}+k x+9=0$ has real and equal roots are :\

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Professor PC Thomas Classes · Answer

(b) : Given equation is $4 x^{2}+k x+9=0$. Since, the equation has real and equal roots.\ ∴ Discriminant, $D=b^{2}-4 a c=0$\ $\Rightarrow k^{2}-4 	imes 4 	imes 9=0 \Rightarrow k^{2}-144=0$\ $\Rightarrow \quad k^{2}=144 \Rightarrow k= \pm 12$\