Question

find the square of the following numbers without actual multiplication. (i) 39 (ii) 42

Answer 1

39^2 = (30 + 9)^2 = 30(30 + 9) + 9(30 + 9)
= 30^2 + 30 * 9 + 9 * 30 + 9^2
= 900 + 270 + 270 +81
= 1521

42^2 = (40 + 2)^2 = 40(40 + 2) + 2(40 + 2)
=40^2 + 40 * 2 + 2 * 40 + 2^2
= 1600 + 80 + 80 + 4
=1764