Question

2x(4x-1)=21
qual é o resultado ? lembrete: é equação de 2°grau

Answer 1

$2x(4x-1)=21$

$8x^2-2x-21=0$

$\Delta=(-2)^2-4\cdot8\cdot(-21)=4+672=676$

$x=\dfrac{-(-2)\pm\sqrt{676}}{2\cdot8}=\dfrac{2\pm26}{16}$

$x'=\dfrac{2+26}{16}=\dfrac{28}{16}=\dfrac{7}{4}$ e $x"=\dfrac{2-26}{16}=\dfrac{-24}{16}=\dfrac{-3}{2}$.

Answer 2

2x(4x-1)=21
2x.4x-2x=21
8x²-2x-21=0

∆=(-2)²-4.8.(-21)
∆=4+32.21
∆=4+672
∆=676

x'=[-(-2)+√676]/2.8=[2+26]/16=28/16=14/8=7/4
x''=[-(-2)-√676]/2.8=[2-26]/16=-24/16=-12/8=-6/4=-3/2

S={-3/2,7/4}