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Identities — MATHS STD 8 — Question

ICSE BoardEnglish MediumSTD 8MATHSIdentities4 Marks
Question
Evaluate : $\left(7 x+\frac{2}{3} y\right)\left(7 x-\frac{2}{3} y\right)$
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Answer

$ \left(7 x+\frac{2}{3} y\right)\left(7 x-\frac{2}{3} y\right)$
$ =7 x\left(7 x-\frac{2}{3} y\right)+\frac{2}{3} y\left(7 x-\frac{2}{3} y\right)$
$ =49 x^2-\frac{14}{3} x y+\frac{14}{3} x y-\frac{4}{9} y$
$ =49 x^2-\frac{4}{9} y^2$

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