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Rezolvati ecuatia:
a)2(x-2)(x+2)+8=x²+9

b)4x²-20x+25=81

Răspuns :

Miky93id
Miky93id Miky93id
a)2(x²-4)+8=x²+9
2x²-8+8=x²+9
2x²=x²+9
2x²-x²=9
x²=9
√x²=√9
|x|=3   ⇒x∈{-3;3}

b)4x²-20x+25-81=0
[(2x-5)-9][(2x-5)+9]=0
(2x-14)(2x+4)=0

2x-14=0   ∧  2x+4=0
2x=14             2x= -4
x=7                    x= -2
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