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Use the Product (A + B) (A – B) = A2 – B2 to Evaluate: 21 X 19 - Mathematics

Sum

Use the product (a + b) (a – b) = a2 – b2 to evaluate:
21 x 19

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Solution

21 x 19 = (20+1) (20−1)

= (20)2 − (1)2

= 400 − 1

= 399

Concept: Product of Sum and Difference of Two Terms
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APPEARS IN

Selina Concise Mathematics Class 8 ICSE
Chapter 12 Identities
Exercise 12 (A) | Q 4.1 | Page 150
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