cho hàm số y = f ( x ) = 4x2 - 7
a)tính f ( 1/2 ); f ( 3 ) ; f ( 0 ) ; f (-2 )
thay f(1/2);f(3);f(0);f(-2) vào hàm số f(x)=4x2-7
f(1/2)=4.(1/2)2-7=-6
f(3)=4.32-7=29
f(0)=4.02-7=-7
f(-2)=4.(-2)2-7=-24
a) \(f\left(\frac{1}{2}\right)=4\cdot\left(\frac{1}{2}\right)^2-7=4\cdot\frac{1}{4}-7=1-7=-6\)
\(f\left(3\right)=4\cdot3^2-7=4\cdot9-7=36-7=29\)
\(f\left(0\right)=4\cdot0^2-7=4\cdot0-7=0-7=-7\)
\(f\left(-2\right)=4\cdot\left(-2\right)^2-7=4\cdot4-7=16-7=9\)
b) Ta có \(f\left(x\right)=93\)nên \(4x^2-7=93\)
=> \(4x^2=93+7\)
=> \(4x^2=100\)
=> \(x^2=100:4=25\)
=> x = 5 hoặc x = -5
