Since a right triangle is formed, the radius of the cross-section is the missing side of the triangle.
Apply the Pythagorean theorem:
C^2 = a^2 + b^2
Where:
c = hypotenuse = 5
a & b = the other 2 legs of the triangle = 4 and x
Replacing:
5^2 = 4^2 + x^2
solve for x ( radius of the cross-section)
25 = 16 + x^2
25-16 = x^2
9 = x^2
√9 = x
x = 3 cm
