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Identities — MATHS STD 8 — Question

ICSE BoardEnglish MediumSTD 8MATHSIdentities4 Marks
Question
Use the direct method to evaluate : $\left(\frac{\mathrm{a}}{2}-\frac{\mathrm{b}}{3}\right)\left(\frac{\mathrm{a}}{2}+\frac{\mathrm{b}}{3}\right)$
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Answer

Note : $(a+b)(a-b)=a^2-b^2$
$\left(\frac{\mathrm{a}}{2}-\frac{\mathrm{b}}{3}\right)\left(\frac{\mathrm{a}}{2}+\frac{\mathrm{b}}{3}\right)$
$ =\left(\frac{\mathrm{a}}{2}\right)^2-\left(\frac{\mathrm{b}}{3}\right)^2$
$ =\frac{\mathrm{a}^2}{4}-\frac{\mathrm{b}^2}{9}$

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