6 1. Express the equation in cartesian coordinate r = 3 cos 0 + 2 sin 0 2. Express the equation in cartesian coordinate r = sec @ tan 0 3. Express the equation in polar coordinate x²(x² + y²) = y² dy 4. Solve the differential equation dx - sec x = 0 5. Solve the differential equation 6. Solve the differential equation 2xy dx + x2 dy = 0 (1+r) dy 7. Solve the differential equation dx y 4y" - 25y = 0 8. Solve the differential equation 9y"-30y+25y = 0