# Thread: Turning point form not showing correct TP? Important and urgent!

1. ## Turning point form not showing correct TP? Important and urgent!

Hey guys,

so I have the function f(x)= -3x2 - 18x - 26.

I've put this into TP form and have gotten (x+3)2 - 1/3

This would lead me to believe that the x turning point is -3 and the y turning point is - 1/3. However, when graphing it using desmos, it shows that the y turning point is 1.

I thought I did something wrong, but using that turning point form, I found the correct x intercepts, so I'm very confused! Can anyone help?

2. ## Re: Turning point form not showing correct TP? Important and urgent!

\begin{align*} f(x) &= -3x^2 - 18x - 26 \\ &= -3\left(x^2 +6x + \dfrac{26}{3}\right) \\ &= -3\left((x+3)^2 - 9 +\dfrac{26}{3} \right) \\ &= -3\left((x+3)^2 - \dfrac{1}{3}\right) \\ &= -3(x+3)^2 +1 \end{align*}

3. ## Re: Turning point form not showing correct TP? Important and urgent!

Originally Posted by AlwaysHufferr
so I have the function f(x)= -3x2 - 18x - 26.

I've put this into TP form and have gotten (x+3)2 - 1/3
Well, you could have substituted, as example, x=2
and seen right away your result is not correct...

4. ## Re: Turning point form not showing correct TP? Important and urgent!

Important fact: f(x) and a * f(x) will always have the same x-intercepts and the same x turning points if a is not zero, but will not have the same y-intercept and will not have the same y turning points unless a is 1.