Question

Use identity to get the product of (7a−9b)(7a−9b)(7a−9b)(7a−9b)

• A. $49a^2-126ab-b^2$
• B. $49a^2-126ab+b^2$
• C. $a^2-126ab+81b^2$
• D. $49a^2-126ab+81b^2$

Answer 1

The correct option is D $49a^2-126ab+81b^2$

$(7a-9b)(7a-9b)$
Using,
$(a-b{)}^2=a^2+b^2-2ab$
$=(7a-9b{)}^2$
$=(7a{)}^2+(9b{)}^2-2\left(7a\right)\left(9b\right)$
$=49a^2+81b^2-126ab$