Question

solve using identity (7a+9b)(-9b)

Answer 1

Answer:

$\sf{49a}^{2}-{81b}^{2}$

Step-by-step explanation:

As the expression is binomial,

Let the first term (7a) be x.

and the second term (9b) be y.

Now,

$\sf(x+y)(x-y)$

$\sf x(x-y)+y(x-y)$

$\sf{x}^{2}-xy+xy-{y}^{2}$

$\sf{x}^{2}-{y}^{2}$

So identity using :-

$\sf{x}^{2}-{y}^{2}$

Solution -

[squaring whole bracket]

= $\sf({7a)}^{2}-({9b)}^{2}$

= $\sf({49a)}^{2}-({81b)}^{2}$