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प्रश्न
Use the product (a + b) (a – b) = a2 – b2 to evaluate:
21 x 19
बेरीज
उत्तर
21 x 19 = (20+1) (20−1)
= (20)2 − (1)2
= 400 − 1
= 399
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Product of Sum and Difference of Two Terms
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