Please help me answer the red underline question below using the theorem in the picture. Clear Step by step answer would be great, thank you

THEOREM 10.7 Parametric Form of the Derivative If a smooth curve C is given by the equations x = f(1) and y = g(t) then the slope of C at (x, y) is dy _ dy/di dx + 0. dx dx/di' di If we differentiate our line y = 2x from Sec 10.2 with respect to x, we get 2. That is, y' = 2. Using Theorem 10.7 above, we see that our parametrization of y = 2x into x =t y = 2t yields the same result. To wit: dy dy _ dt _2 dx = = 2 dx dt The arc length that we learned in Sec 7.4 has its correspondence in parametric form. We may interpret this arc length as the distance which the moving object covers while tracing the arc. THEOREM 10.8 Arc Length in Parametric Form If a smooth curve C is given by x = f(1) and y = g(1) such that C does not intersect itself on the interval a s t s b (except possibly at the endpoints), dy _di _2-2 dx dx dt The arc length that we learned in Sec 7.4 has its correspondence in parametric form. We may interpret this arc length as the distance which the moving object covers while tracing the arc. THEOREM 10.8 Arc Length in Parametric Form If a smooth curve C is given by x = f(1) and y = g(1) such that C does not intersect itself on the interval a s t s b (except possibly at the endpoints), then the arc length of C over the interval is given by This formula in parametric form (Theorem 10.7 above) can actually be derived from the arc length formula we had in Sec 7.4, which was used in the last application problem in Exam 1 and I reproduce here below. - [ VI +V'()F dx Bonus points await anyone who could show how the parametric form in Theorem 10.7 is obtained from this arc length formula. The area of a surface of revolution generated by a curve in parametric form concludes this section (Theorem 10.9). See how the formula below parallels that of the area of a surface of revolution in Sec 7.4. Observe closely how the radius of revolution changes according to the axis of revolution