Question

Prove: If n is a positiveinteger and n2 is divisible by 3, then n is divisible by3.

Answer 1

Answer:

If $n^2$ is divisible by 3, the n is also divisible by 3.

Step-by-step explanation:

We will prove this with the help of contrapositive that is we prove that if n is not divisible by 3, then, $n^2$ is not divisible by 3.

Let n not be divisible by 3. Then $\frac{n}{3}$ can be written in the form of fraction $\frac{x}{y}$, where x and y are co-prime to each other or in other words the fraction is in lowest form.

Now, squaring

$\frac{n^2}{9} = \frac{x^2}{y^2}$

Thus,

$n^2 = \frac{9x^2}{y^2}$

$\frac{n^2}{3} = \frac{3x^2}{y^2}$

It can be clearly seen that the fraction $\frac{3x^2}{y^2}$ is in lowest form.

Hence, $n^2$ is not divisible by 3.

Thus, by contrapositivity if $n^2$ is divisible by 3, the n is also divisible by 3.