Using the identity ${\left(a+b\right)}^2=a^2+b^2+2ab$ or ${\left(a-b\right)}^2=a^2+b^2-2ab$, find the square of the number $399$.

Write a Pythagorean triplet whose smallest number is $16$.

Write a Pythagorean triplet whose smallest number is $6$.

Write a Pythagorean triplet whose smallest number is $14$.

Write a Pythagorean triplet whose smallest number is $8$.

Write a Pythagorean triplet one of whose number is $16$.

Write a Pythagorean triplet one of whose number is $35$.

Write a Pythagorean triplet one of whose number is $17$.

Using repeated subtraction method, find the square root of the following number.

$144$