Question

Which of the following identity is not applicable to simplify ${(4x+5y)}^2$ - ${(5x+4y)}^2$?

• A. = + 2ab +
• B. - = (a + b)(a - b)
• C. = - 2ab +
• D. Both A and B

Answer 1

Answer: (A), (C)

The correct options are
A

= + 2ab +

C

= - 2ab +

Using Identity $a^2$ - $b^2$ = (a+b)(a-b)
${(4x-5y)}^2$) - ${(5x+4y)}^2$ = [(4x + 5y) - (5x + 4y)] $\times$ [(4x + 5y) + (5x + 4y)]
$=(y-x)(9x+9y)$
$=9xy-$ 9$x^2$ + 9$y^2$$-9xy$
= 9$y^2$ - 9$x^2$