6. sometimes the second order differential equation pqy=r can be transformed to dx an integrable form by (a) by changing the dependent variable (b) by changing

6. Sometimes the second order differential equation PQy=R can be transformed to dx an integrable form by (a) by changing the dependent variable (b) by changing the independent variable (c) by interchanging the dependent and independent variable (d) none of the above 7. For solving the second order differential equation +p+Qy= R, variation of d parameter method is applied when (a) both CF and PI cannot be obtained easily b) PI is known easily but CF cannot be obtained easily (C) CF is known easily but PI cannot be obtained easily (d) none of the above