For what value of the constant a does the substitution u = ya converts the differential equation -t 2y' — e¯¹ y = (ty) ³/2 into a linear first order differential equation in u ? О a = -1/2 О О a = = 3/2 a = О ○ a = -3/2 a = 5/2 О ○ a = = −5/2 a = = 1/2