how to find axis of symmetry?

Question

#1. y=x^2-8x-9

#2. y=3x^2-9x+5

Answer 1

Try to complete the square
1)y= (x-4)^2 -25 If you change x-4into 4-x y doesn´t change so

x=4 is an axis of symmetry

2)y=3(x^2-3x+5/3) = (x-3/2)^2 -7/12 .By the same reason as above x=3/2 is axis of symmetry

Answer 2

Question1
y = (x² - 8x + 16) - 16 - 9
y = (x - 4)² - 25
Axis of symmetry is x = 4

Question 2
y = 3(x² - 3x + 5/3)
y = 3 (( x² - 3x + 9/4) - 9/4 + 5/3))
y = 3((x - 3/2)² - 7/12)
Axis of symmetry is x = 3/2

Answer 3

Hey if u know differentiation t could be done like this
Since it is a function in x
put dy/dx=0 to get the axis of symmetry
i.e. in case 1
2x-8=0
or x=4 is the line of symmetry
case2
6x-9=0
or x=3/2 is the line of symmetry.