Question

A forma fatorada de x²-4x-21 é:
(x+3).(x+7)
(x-3).(x-7)
(x+3).(x-7)
(x-3).(x+7)

Answer 1

$(x+3).(x+7) \\ x^{2}+7x+3x+21 \\ x^{2}+10x+21$  Errada


$(x-3).(x-7) \\ x^{2} -7x-3x+21 \\ x^{2}-10+21$ Errada

$(x+3).(x-7)\\ x^{2} -7x+3x-21 \\ x^{2} -4x-21$ Correta

$(x-3).(x+7) \\ x^{2} -7x-3x-21 \\ x^{2} -10x-21$ Errada