also

print(f"{(3**2 + 5**2)**(1/3) = }")

output:

(3**2 + 5**2)**(1/3) = 3.239611801277483

doubling Jerrybibo's comment that generally eval is evil! (and thanks for mentioning about not eval()'ing an input) if you need to reuse the string of b_equation and / or the result b, then eval() seems legit

b_equation = "(3**2 + 5**2)**(1/3)"
b = eval(b_equation)
print(f"{b_equation} = {b}")

# use b_equation and / or b for stuff