JEE MAIN - Mathematics (2025 - 23rd January Morning Shift - No. 23)
If the equation $\mathrm{a}(\mathrm{b}-\mathrm{c}) \mathrm{x}^2+\mathrm{b}(\mathrm{c}-\mathrm{a}) \mathrm{x}+\mathrm{c}(\mathrm{a}-\mathrm{b})=0$ has equal roots, where $\mathrm{a}+\mathrm{c}=15$ and $\mathrm{b}=\frac{36}{5}$, then $a^2+c^2$ is equal to _________
Answer
117
Explanation
$$\begin{aligned}
&a(b-c) x^2+b(c-a) x+c(a-b)=0\\
&\mathrm{x}=1 \text { is root } \therefore \text { other root is } 1\\
&\begin{aligned}
& \alpha+\beta=-\frac{b(c-a)}{a(b-c)}=2 \\
& \Rightarrow-b c+a b=2 a b-2 a c \\
& \Rightarrow 2 a c=a b+b c \\
& \Rightarrow 2 a c=b(a+c) \\
& \Rightarrow 2 \mathrm{ac}=15 \mathrm{~b} \ldots(1) \\
& \Rightarrow 2 \mathrm{ac}=15\left(\frac{36}{5}\right)=108 \\
& \Rightarrow \mathrm{ac}=54 \\
& \mathrm{a}+\mathrm{c}=15 \\
& \mathrm{a}^2+\mathrm{c}^2+2 \mathrm{ac}=225 \\
& \mathrm{a}^2+\mathrm{c}^2=225-108=117
\end{aligned}
\end{aligned}$$
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