Question

6-Dada a função f(x) = x³ + 3x² - 2x - 9, o valor de f(1) + f(-2), é:

(a) 2

(b) -8

(c) 6

(d) -4​

Answer 1

$\sf f(1)~+~f(-2)~=~\underbrace{\sf\left(x^3~+~3x^2~-~2x~-~9\right)}_{para~x~=~1}~+~\underbrace{\sf\left(x^3~+~3x^2~-~2x~-~9\right)}_{para~x~=\,-2}$

$\sf f(1)~+~f(-2)~=~\left(1^3~+~3\cdot 1^2~-~2\cdot 1~-~9\right)~+~\left((-2)^3~+~3\cdot (-2)^2~-~2\cdot (-2)~-~9\right)$

$\sf f(1)~+~f(-2)~=~\left(1~+~3\cdot 1~-~2~-~9\right)~+~\left(-8~+~3\cdot 4~+~4~-~9\right)\\\\\\\sf f(1)~+~f(-2)~=~\left(1~+~3~-~2~-~9\right)~+~\left(-8~+~12~+~4~-~9\right)\\\\\\\sf f(1)~+~f(-2)~=~\left(4~-~11\right)~+~\left(4~-~5\right)\\\\\\\sf f(1)~+~f(-2)~=~\left(-7\right)~+~\left(-1\right)\\\\\\\sf f(1)~+~f(-2)~=\,-7~-~1\\\\\\\boxed{\sf \sf f(1)~+~f(-2)~=\,-8}~~\Rightarrow~Letra~B$

$\Huge{\begin{array}{c}\Delta \tt{\!\!\!\!\!\!\,\,o}\!\!\!\!\!\!\!\!\:\,\perp\end{array}}Qualquer~d\acute{u}vida,~deixe~ um~coment\acute{a}rio$