Question

18) Se f(x) = = ax + b, tendo f(1) = 3 e f(3) = 9, determine o valor de f(-2).
-9
-6
-3
3
6
alguém me ajuda pfvrrrrr

Answer 1

$f(x)=ax+b\\\\f(1)=ax+b\\f(1)=a+b\\3=a+b\\\\f(3)=ax+b\\f(3)=3a+b\\9=3a+b\\\\\\\left\{ \begin{array}{c} a+b=3 \\ 3a+b=9 \end{array}\right.\\\\\left\{ \begin{array}{l} a+b=3 \mbox{ } (-1) \\ 3a+b=9 \end{array}\right.\\\\\left\{ \begin{array}{l} -a-b=-3 \\ 3a+b=9 \end{array}\right.\\\\3a-a=9-3\\2a=6\\a=3\\\\a+b=3\\3+b=3\\b=0\\\\f(x)=3x+0\\f(-2)=3(-2)+0\\f(-2)=-6$