Question

41*39Find the value using expansion formula.

Answer 1

BONJOUR,
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we can write this like (40+1)(40-1)
then, we use identity
(a+b)(a-b) = a^2- b ^2
$(40 + 1)(40 - 1) \\ = (40) { }^{2} - 1 {}^{2} \\ = 1600 - 1 \\ = 1599$