Question

quem me responder corretamente ganha os 10 pontos 
a) 2x(4x-1)=21
b) x(x-2)+6=4(x+1)

Answer 1

a)
2x(4x-1)=21
8x²-2x=21
8x²-2x-21=0

(E aplica bhaskara)

b)
 x(x-2)+6=4(x+1)
x²-2x+6=4x+1
x²-2x+6-4x-1=0
x²-6x+5=0

(E aplica bhaskara)

Answer 2

a) 2x(4x-1)=21
$8x^2-2x-21=0 \\ \\ \Delta=(-2)^2-4.8.(-21) 4+672=676 \\ \\ x=\frac{2+-26}{16} \\ \\ x_1=\frac{28}{16}=\frac{7}{4} \\ \\ x_2=-\frac{24}{16}=-\frac{3}{2}$

b) x(x-2)+6=4(x+1)
$x(x-2)+6=4(x+1) \\ \\ x^2-2x+6=4x+4 \\ \\ x^2-2x-4x+6-4=0 \\ \\ x^{2} -6x+2=0 \\ \\ \Delta=(-6)^2-4.1.2=36-8=28 \\ \\ x=\frac{6+-\sqrt{28}}{2}=\frac{6+-2\sqrt7}{2}=3+-\sqrt7$