4-4. Determine the variations of the functionals: (a) J(x) = {“ [x³(t) − x²(t)x(t)] dt. (b) J(x) = ƒ" [x}(t) + x₁(1)x2(t) + ×¥(s) + 2x₁(t)*₂(1)] dt. (c) J(x) = ["ex) dt. Assume that the end points are specified.