f(x) = -2x² + 20x - 42
This is a quadratic expression.
For a general expression ax² + bx + c, the axis of symmetry x = -b/2a
Comparing -2x² + 20x - 42 to ax² + bx + c, a = -2, b = 20, c= -42
Axis of symmetry, x = -b/2a
x = -20 / (2 * -2) = -20/-4 = 5
Therefore axis of symmetry is x = 5.
