Line Integral calculating the ds

Question

Doesn't change the result, but why in the last steps constant in front of the integral is 9 and not 27? Where did the 9 that came from squaring the dx/dt and dy/dt go?

Answer 1

They forgot it. The first line of step 4 should have been:

$$\text{Area} = \int_{t = 0}^{t = \pi} (3 \sin(t))(3 \cos(t)) \sqrt{(-3\sin(t))^2 + (3\cos(t))^2} $$