Question

determinar os valores de x para q o determinante seja nulo

Answer 1

((3x).(x+3))-(3.4)=0

3x²+9x-12=0 (/3)
x²+3x-4=0

$x= \frac{-b \frac{+}{} \sqrt{b^2-4ac} }{2a} \\ \\ x= \frac{-3 \frac{+}{} \sqrt{3^2-4.1.(-4)} }{2.1} \\ \\ x= \frac{-3 \frac{+}{} \sqrt{9+16} }{2} \\ \\ x= \frac{-3 \frac{+}{} \sqrt{25} }{2} \\ \\ x= \frac{-3 \frac{+}{}5 }{2} \\ \\ x'= \frac{-3+5}{2} = \frac{2}{2} = 1 \\ \\ x''= \frac{-3-5}{2}= \frac{-8}{2}=-4 \\ \\ S=[1; -4]$