agentkronus agentkronus

02-03-2015
Mathematics

contestada

Find x when P = 21.

P = x(x - 1) / 2

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konrad509 konrad509

02-03-2015

[tex]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[/tex]

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