The system of first-order ODEs dx/dt=y, dy/dt=3x+t²-cos(2t) is equivalent to the second-order ODE x''+a(t) x'+b(t) x=c(t) with:
a) a(t) = 3t² - cos(2t) , b(t) = 1, c(t) = 0
b) a(t) = 1, b(t) = 3t² - cos(2t) , c(t) = 0
c) a(t) = 0, b(t) = 3t² - cos(2t) , c(t) = 1
d) a(t) = 0, b(t) = 1, c(t) = 3t² - cos(2t)