Q3 of 157 Page 22

Using the identity (x + a)(x + b) = x2 + (a + b)x + ab, find out the following products:

(7x + 3y) (7x – 3y)

Given (7x + 3y) (7x – 3y)


Using (x + a)(x + b) = x2 + (a + b)x + ab


(7x + 3y) (7x – 3y)= (7x)2 + (3y – 3y)7x + 3y×3y


⇒ (7x + 3y) (7x – 3y) = 49x2 – 9y2


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