Question

02. As raízes da função, definida em R, dada por f(x) = -x² + 3x + 28, são: *
a)x1=121 /x2=3
b)x1=28/x2=3
c)x1=4/x2=-7
d)x1=-4/x2=7​

Answer 1

$\large\boxed{\begin{array}{l}\sf -x^2+3x+28=0\\\sf\Delta=b^2-4ac\\\sf\Delta=3^2-4\cdot(-1)\cdot28\\\sf\Delta=9+112\\\sf\Delta=121\\\sf x=\dfrac{-b\pm\sqrt{\Delta}}{2a}\\\sf x=\dfrac{-3\pm\sqrt{121}}{2\cdot(-1)}\\\sf x=\dfrac{-3\pm11}{-2}\begin{cases}\sf x_1=\dfrac{-3+11}{-2}=\dfrac{8}{-2}=-4\\\sf x_2=\dfrac{-3-11}{-2}=\dfrac{-14}{-2}=7\end{cases}\\\huge\boxed{\boxed{\boxed{\boxed{\sf\maltese~alternativa~d}}}}\end{array}}$

Answer 2

Explicação passo-a-passo:

-x² + 3x + 28

a=-1

b=3

c=28

∆=b²-4ac

∆=3²-4×-1×28

∆=9+112

∆=121

-b±√∆/2a

-3±√121/2×-1

-3±11/-2

x¹=-3+11/-2=8/-2=-4

x²=-3-11/-2=-14/-2=+7

Alternativa "D"