Q. 5 I5.0( 2 Votes )

Evaluate the following by using the identities:

81 × 79

Answer :

81 × 79= (80 + 1) (80 – 1)


We know that


(a2 – b2) = (a – b) × (a + b)


(80 + 1) (80 – 1) = (80)2 – (1)2


(80 + 1) (80 – 1) = 6400 – 1 = 6399


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