Question

89^2= ____

(a) (90-1)^2

(b) 90^2

(c) 1^2

(d) 9^2

The question was posed to me in an international level competition.

My question is based upon Finding the Square of a Number in chapter Squares and Square Roots of Mathematics – Class 8

Answer 1

The correct option is (a) (90-1)^2

For explanation I would say: If we have to find the square of the number which is near 0 we use the second variation i.e. (90-1)^2. This would help us and make the calculations easier.

Therefore (90-1)^2= 90^2-2×90×1+1^2

Therefore (90-1)^2= 8100-180+1

Therefore (90-1)^2=7921.