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Question
Using (x + a) (x + b) = x2 + (a + b) x + ab, find 9.7 × 9.8
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Solution
9.7 × 9.8 = (10 − 0.3) (10 − 0.2)
= (10)2 + [(− 0.3) + (− 0.2)] (10) + (− 0.3) (− 0.2)
= 100 + (− 0.5)10 + 0.06 = 100.06 − 5 = 95.06
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