Question

How do you do this problem?

Answer 1

The pythagorean theorem states that a² + b² = c². 
We have a = 10 and c = 20. 
100 + b² = 400 
Subtract 100 from each side. 
b² = 300 
Get the square root of 300. 
It could be expressed as b ≈ 17.321, or could stay in radical form as$\sqrt{300}$. 
Hope this helps!