a) Ta có hàm số $y=f(x)=1-4x^{2}$
1. $y=f(1)=1-4.1^{2}=1-4.1=1.4=-3$
$→f(1)=-3$
2. $y=f(-2)=1-4.(-2)^{2}=1-4.4=1-16=-15$
$→f(-2)=-15$
3. `y=f(\frac{1}{5})=1-4.\frac{1}{5}=1-\frac{4}{5}=\frac{5}{5}-\frac{4}{5}=\frac{1}{5}`
`→f(\frac{1}{5})=\frac{1}{5}`
4. `y=f(\frac{-3}{5}=1-4.\frac{-3}{5}=1-\frac{-12}{5}=\frac{5}{5}-\frac{-12}{5}=\frac{17}{5}`
`→f(\frac{-3}{5})=\frac{17}{5}`
b) Ta có y=1:
$1=1-4.x^{2}$
$⇔ 4.x^{2}=0$
$⇔ x^{2}=0$
$⇒ x=0$
Ta có y=0
$0=1-4.x^{2}$
$⇔ 4.x^{2}=1$
$⇔ x^{2}=4$
$⇔ x=\sqrt{4}$
$⇒ x=2$
Ta có y=10:
$10=1-4.x^{2}$
$⇔ 4.x^{2}=-9$
`⇔ x^{2}=\frac{-9}{4}`
`⇔ x=\sqrt{\frac{-9}{4}}`
`⇒ x=\frac{3}{2}`
