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Brums [2.3K]
3 years ago
14

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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