Question

Evaluate the following product without multiplying directly 77×79

Answer 1

77 × 79

= (80-3) (80-1)

[(x-a) (x-b) = x² - (a+b)x +ab

= 80² - {(-3-1)*80} + (-3 × -1)

= 6400 + 320 +3

= 6723

Answer 2

The answer is, 6083

Given : The given multiplication work is (77×79)

To find : The answer to the given multiplication, without multiplying.

Solution :

We can simply solve this mathematical problem by using the following mathematical process. (our goal is to evaluate the answer without doing the multiplication)

Here, we have to use identities to solve the problem without any major calculation.

So,

= 77 × 79

= (80-3) × (80-1)

= (80)² - (3+1)×80 + (3×1)

= 6400 - 320 + 3

= 6400 - (320 - 3)

= 6400 - 317

= 6083

(This will be considered as the final result.)

Used formula :

• (x-a) (x-b) = x² - (a+b) × x + (ab)

Hence, the answer is 6083