Evaluate the line integral integral_c nabla phi middot dr for the following function phi and oriented curve c (a) using a parametric description of c and evaluating the integral directly, and (b) using the fundamental theorem for line integrals. phi(x, y) = xy; c: r(t) = (cos t, sin t), for 0 lessthanorequalto t lessthanorequalto pi/2 (a) set up the integral used to evaluate the line integral using a parametric description of c. use increasing limits of integration. integral^pi/2 (cos 2t) dt (type exact answers.) (b) select the correct choice below and fill in the answer box(es) to complete your choice. (type an ordered pair. type an exact answer for each coordinate, using radicals as needed.)
a. if b is the last point on the curve, then the value of the line integral is phi(b).
b. if a is the first point on the curve, and b is the last point on the curve, then the value of the line integral is phi(b) - phi(a).
c. if a is the first point on the curve, then the value of the line integral is phi(a).
d. if a is the first point on the curve, and b is the last point on the curve, then the value of the line integral is phi(a) - phi(b).