You can put this solution on YOUR website! start with 36x^2 - 81 = y
set y = 0 to get 36x^2 - 81 = 0
add 81 to both sides of this equation to get 36x^2 = 81
divide both sides of this equation to get x^2 = 81/36
simplify to get x^2 = 2.25
take the square root of both sides of the equation to get x = 1.5 or x = -1.5
this is also in the form of (a^2 - b^2) = (a + b) * (a - b)
a^2 = 36x^2 so a = 6x
b^2 = 81 so b = 9
you get (36x^2 - 81) = ((6x)^2 - 9^2) = (6x + 9) * (6x - 9)
set each of these factors equal to 0 and you get 6x = -9 and 6x = 9
solve for x in each to get x = -1.5 and x = 1.5
you could also have used the quadratic formula which would have gotten you the same answer.
the equation of 36x^2 - 81 = 0 yields:
a = 36
b = 0
c = -81
the quadratic formula is x = (-b plus or minus sqrt(b^2-4ac)) divided by 2a.
solve it and you will see that x = plus or minus 1.5.
