Question

Evaluate each of the following using proper identity : 51 x 57

Answer 1

2907.

51 × 57

= ( 50 + 1 ) × ( 50 + 7 )

= 50^2 + 50 × ( 1+7 ) + (1 × 7)

{ By (x+a)(x+b) = x^2 + x ( a+b ) + ab }

= 2500 + (50 × 8) + 7.

= 2500 + 400 + 7.

= 2907.