Describe the given set in cylindrical coordinates. a. x² + y² ≤ 9, x ≥ y b. y² + z² ≤ 4, x = 0 c. x² + y² + z² = 4, x ≥ 0, y ≥ 0, z ≥ 0 d. x² + y² ≤ 1,0 ≤ z ≤ 2