Explanation:
they are parabolas.
their line of symmetry is exactly in the middle between their x-intercepts (when y = 0).
these x-intercepts we get from the factors : y can only be 0, when at least one of the factors is 0.
y = (x + 14)(x + 16)
means y = 0, when x = -14 or x = -16.
so, the line of symmetry is
x = -15
y = (x - 12)(x - 18)
y = 0, when x = 12 or x = 18
line of symmetry is
x = 15
y = (x + 13)(x - 17)
x = -13 or x = 17
line of symmetry
x = 2 (again, the middle between -13 and +17)
y = (x - 10)(x + 20)
x = 10 or x = -20
line of symmetry
x = -5