Question

Ao calcular a multiplicação (x+2).(2x+1) obtem-se?

Answer 1

(x+2). (2x+1)=
2
2x+x.4x+2=
2 2
2x +4x +2
4
8x + 2

Answer 2

$(x+2).(2x+1) \to 2 x^{2} +x+4x +2=0 \to 2 x^{2} +5x+2=0\\ \\a=2;b=5;c=2\\\\ \Delta= b^{2} -4.a.c \to \Delta= 5^{2} -4.2.2\to \Delta=25-16 \to \Delta=9 \\ \\ x= \frac{-b+- \sqrt{\Delta} }{2.a} \to x= \frac{-5+- \sqrt{9} }{2.2} \to x= \frac{-5+-3}{4} \\ \\ x'= \frac{-5+3}{4} \to x'= \frac{-2}{4} \to x'= -\frac{1}{2} \\ \\ x''= \frac{-5-3}{4} \to x''= \frac{-8}{4} \to x''=-2 \\ \\ \\ S=(-\frac{1}{2} ;-2)$