Answer:
x² × 2
Explanation:
Notice vocabulary:
- twice → multiplication by a factor of two → ×2
- a number → unknown number; variable → x
- the square → raised to the power of two → x²
Put this information together.
"Twice the square of a number"
Since it says of a number, this number comes first →

"Twice the square of a number"
The square of a number means that the variable will be squared →

"Twice the square of a number"
Multiply the variable by a factor of two →

:Done