In each case, does the given set of functions form a fundamental set of solutions to the given linear homogeneous differential equation? Why or why not? Justify your answer using direct evaluation of the solutions and the Wronskian.
a) {sin(2x), cos(2x)} for y" + 4y = 0
b) {cosh(2x), sinh(2x)} for y" - 2y = 0
c) {e^-3x, 4e^-3x} for y" + 6y' + 9y = 0