looks like an elliptic integral.
plus, your parentheses are mismatched.
How do I evaluate this integral?
integral from 0 to 24 of the √(1+[(π/3)*cos((πx/3)]^2)
3 answers
integral from 0 to 24 of the √(1+[(π/3)*cos(πx/3)]^2)dx
29.6