Answer:
D: √(-4)
Step-by-step explanation:
D: √(-4) is not a real number; it's an imaginary one.
Given problem;
A = 4 π R²
To solve for R, we have to make it the subject of the expression.
Since
A = 4 π R² , follow these steps to find R;
Multiply both sides by
A x
=
x 4 π R²
= R²
Then find the square root of both sides
√R² =
R = 
The solution is 
Step-by-step explanation:

Answer:
10
Step-by-step explanation:
5! divided by all the repeats so 3!2! = 10 ways
ln(20) + ln(5) = 2 ln(<em>x</em>)
ln(20×5) = ln(<em>x</em> ²)
ln(100) = ln(<em>x</em> ²)
100 = <em>x</em> ²
<em>x</em> = 10