Respostas

2014-04-27T09:19:08-03:00
(x-9)^2 - 4 = 21
x^2-18x+81-4 = 21
x^2-18x+56=0
Δ=324-4×1×56
Δ=100
x1=18-√100÷2= 4
x2=18+√100÷2=14
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2014-04-27T10:54:07-03:00
(x-9)² - 4 = 21
(x-9)² = 25 portanto
x-9 = 5 ==> x = 14 ou
x-9 = -5 ==> x = 4
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