Question

Which of the following is not an irrational number?​

• A. $17-\sqrt{23}$
• B. $13+\sqrt{1521}$
• C. $41\sqrt{7}$
• D. $17+\sqrt{23}$

Answer 1

The correct option is B $13+\sqrt{1521}$

$\sqrt{23}$ and $\sqrt{7}$ are not a perfect square and hence its an irrational number. so, $17+\sqrt{23}$, $17-\sqrt{23}$, and $41\sqrt{7}$ are irrational numbers.
$\sqrt{1521}$ = 39, hence $13+\sqrt{1521}$ = 52, which is a rational number.