The axis of symmetry is also defined by the following equation:

x= -b/2a

Remember, a quadratic function has the following form:

y=ax^{2}+bx+c

Follow 4 steps to use an equation to calculate the line of symmetry for *y* = *x*^{2} + 2*x*

- Identify
*a*and*b*for*y*=**1***x*^{2}+**2***x*.**a = 1; b = 2** - Plug into the equation
*x*= -*b*/2*a.***x = -2/(2*1)** - Simplify.
**x = -2/2** - The line of symmetry is
.*x*= -1