Question

evaluate the (399)^2

Answer 1

$(399)^2$
$=(400-1)^2$
$=(400)^2 + (1)^2+2 (400)(1)$
$=(160000)+ (1)+(800)$
$=160801$

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Answer 2

399^2 = (400 - 1)^2. [identity (a - b)^2 = a^2 + b^2 - 2ab]
= 400^2 + 1^2 - 2×1×400
= 1600 + 1 - 800
= 801