Simplify the following: 1. sqrt(12) 2. sqrt(18)/sqrt(1) 3. cubert(18) * 3sqrt(7) 4. sqrt(26/4)

$$
12 = 4 \times 3
$$

$$
\sqrt{12} = \sqrt{4 \times 3} = \sqrt{4} \times \sqrt{3}
$$

$$
\sqrt{4} = 2
$$
$$
2 \times \sqrt{3} = 2\sqrt{3}
$$
The simplified expression is $\boxed{2\sqrt{3}}$.

$$
\sqrt{9} = 3
$$

$$
\frac{\sqrt{18}}{3} = \frac{\sqrt{9 \times 2}}{3} = \frac{\sqrt{9} \times \sqrt{2}}{3}
$$

$$
\frac{3\sqrt{2}}{3} = \sqrt{2}
$$
The simplified expression is $\boxed{\sqrt{2}}$.

$$
\sqrt[3]{\frac{3}{7}} = \frac{\sqrt[3]{3}}{\sqrt[3]{7}}
$$

$$
\frac{\sqrt[3]{3}}{\sqrt[3]{7}} \times \frac{\sqrt[3]{7^2}}{\sqrt[3]{7^2}} = \frac{\sqrt[3]{3 \times 49}}{\sqrt[3]{7^3}}
$$

$$
\frac{\sqrt[3]{147}}{7}
$$
The simplified expression is $\boxed{\frac{\sqrt[3]{147}}{7}}$.

$$
\sqrt{\frac{26}{4}} = \frac{\sqrt{26}}{\sqrt{4}}
$$

$$
\sqrt{4} = 2
$$

$$
\frac{\sqrt{26}}{2}
$$
The simplified expression is $\boxed{\frac{\sqrt{26}}{2}}$.