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3 years ago

Find x when P = 21. P = x(x - 1) / 2

Mathematics

1 answer:

Kruka [31]3 years ago

8 0

$21=\dfrac{x(x-1)}{2}\\
42=x^2-x\\
x^2-x-42=0\\
x^2+6x-7x-42=0\\
x(x+6)-7(x+6)=0\\
(x-7)(x+6)=0\\
x=7 \vee x=-6$

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