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4. Convert the initial-value problem r(4) + 3r" - sin(t) r' + 8x =+2 x(0) = 1 I'(0) = 2 I"(0) = 3 I'(0) =4 into a system of first order ordinary differential equations with initial values. d'x Note: r 5. Find the following partial derivatives: 2x cos(2t + 1) (a) ut given that u(x, t) = 5t2 (b) upt given that u(x, t) = 5t sin(2xt ) - In 3t - 3vets