Question

Cho hàm số y= 3x^2-1

a) Tính f(-2)

b)Tìm x biết f(x)=47

Answer 1

a)
\(f\left(-2\right)=3.\left(-2\right)^2-1=3.4-1=12-1=11\)

b)

\(f\left(x\right)=3x^2-1=47\)

\(\Leftrightarrow3x^2=47+1=48\)

\(\Leftrightarrow x^2=48:3=16\)

\(\Rightarrow\orbr{\begin{cases}x=4\\x=-4\end{cases}}\)

Answer 2

\(a.f\left(-2\right)=3\left(-2\right)^2-1\)

\(=12-1=11\)

\(b.3x^2-1=47\)

\(=>3x^2=48\)

\(=>x^2=16\)

\(=>x=4or-4\)