y = 2x² - 12x + 21 = 2(x² + 6x) + 21.
Using the complet the square method, you get:
2(x² + 6x) + 21 = 2(x² + 6x + 9) - 2*9 + 21 = 2(x + 3)² + 3.
So the axis of symmetry is: x = -3.
The vertex is: (-3, 3)
Answer: 2(x + 3)² + 3
Explanation: Axis of symmetry: x = -3 Vertex: (-3, 3)
