Math Chapter Wise Ordinary And Partial Differential Equations, Integral Equations And Calculus Of Variations English MCQ DSE TGT 2019 Q.If for 'A' and 'B' are two parameters, y = A cos 3x + B sin 3x, then Ax dy/dx + y = 0 Bd2 y/dx2 + 9y = 0 Cd2 y/dx2 + x2 y= 0 D(x2 – y2) dy/dx - 2 xy = 0 Show answer Correct answer: d2 y/dx2 + 9y = 0