Question

Cho hàm số y = f(x) = 1 - 5x

a) Tính: f(1) ; f(-2) ; f(\(\dfrac{1}{5}\)) ; f(\(-\dfrac{3}{5}\))

b) Tìm x biết f(x) = -4

Answer 1

a) \(y=f\left(x\right)=1-5x\)

\(y=f\left(1\right)=1-5.1=1-5=-4\)

\(y=f\left(-2\right)=1-5.\left(-2\right)=1-\left(-10\right)=1+10=11\)

\(y=f\left(\dfrac{1}{5}\right)=1-5.\dfrac{1}{5}=1-1=0\)

\(y=f\left(\dfrac{-3}{5}\right)=1-5.\left(\dfrac{-3}{5}\right)=1-\left(-3\right)=1+3=4\)

b) \(y=f\left(x\right)=1-5x=-4\)

\(\Rightarrow5x=1-\left(-4\right)\)

\(\Rightarrow5x=1+4\)

\(\Rightarrow5x=5\)

\(\Rightarrow x=\dfrac{5}{5}=1\)

Vậy \(f\left(x\right)=-4\) thì \(x=1\)