Expand : (1 y +4 ) (1 y -9 ) - Vidyadip

Question

Expand :$\left(\frac{1}{y}+4\right)\left(\frac{1}{y}-9\right)$

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Answer

$\begin{aligned} & \text {}\left(\frac{1}{y}+4\right)\left(\frac{1}{y}-9\right) \\ & =\left(\frac{1}{y}\right)^2+(4-9) \frac{1}{y}+4 \times(-9) \\ & \quad \ldots\left[\because(x+a)(x+\mathrm{b})=x^2+(a+b) x+a b\right] \\ & =\frac{1}{y^2}-\frac{5}{y}-36\end{aligned}$

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