Question
Factorise: $81-49 \mathrm{x}^2$
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Answer
$81-49 \mathrm{x}^2$
$=(9)^2-(7 \mathrm{x})^2=(9+7 \mathrm{x})(9-7 \mathrm{x})$
$\{\because a^2- b^2= (a + b)(a - b)\}$
$=(9)^2-(7 \mathrm{x})^2=(9+7 \mathrm{x})(9-7 \mathrm{x})$
$\{\because a^2- b^2= (a + b)(a - b)\}$
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