Q5 of 157 Page 22

Evaluate the following by using the identities:

9.7 × 9.8

Given 9.7 × 9.8 = (9 + 0.7)(9 + 0.8)


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


(9 + 0.7)(9 + 0.8) = (9)2 + (0.7 + 0.8)9 + (0.7)×(0.8)


⇒ 9.7 × 9.8 = 81 + 13.5 + 0.56


⇒ 9.7 × 9.8 =95.06


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