Thank you! (For (d) you don't have to graph it on a coordinate plane if it's too inconvenient, please just explain where I need to graph!)

 Apr 23, 2021



You can graph it out with desmos. https://www.desmos.com

x intercepts are when y = 0, when y = 0, the x coordinates are -4 and 1. 

y intercepts are when x = 0, which is 4. 


Try to see if you can find the vertex and axis by yourself. :))

You can also see by graphing it in desmos. 



 Apr 23, 2021

Thanks so much for the explanation and references, it really helps! :)

Corduroy  Apr 23, 2021

You're welcome :)



catmg  Apr 23, 2021

Hi again!


I spent some time trying to solve this problem but I am a little confused. Could you show me how you got the x and y intercepts? I'm not sure how you got to -4 and 1. I'm sorry I'm new to this :(

Corduroy  Apr 24, 2021

Hi Cordueroy,  catmg has given you a good answer but I am happy to discuss it with you.


This question is poorly written because the formula has f(x) but you are asked for y.

You just need to understand that  y=f(x)





Think about the y axis, what are some points on the y axis? 

(0,6), (0,-2) (0,7) .... etc,    What do they all have in common?   well the x value is always 0.

SO,  the equation of the y axis is  x=0

So to find the y intercept, that is where it crosses the y axis, you must solve the equation simultaneously with x=0.

that might sound complicated but it is not.

Just substitute the x in the equation with 0,  like this

\(f(0)=-(0+4)(0-1)\\ f(0)=-+4*-1\\ f(0)=+4 \)


So the y intercept (which should really be called the f(x) intercept) is 4


the x axis has the equation y=0     f(x)=0

To find the x intercept you have to solve   




Two terms will only multiply to give 0 if one or both of them is equal to 0 so


\(x+4=0\quad \rightarrow \quad x=-4\\or\\ x-1=0\quad \rightarrow \quad x=+1\)


so the x intercepts are   -4 and 1



This is a concave down parabola. 

I know that it is a parabola because  the highest power of x, if you multiply it out is 2     (x^2) 

And I know it is concave down because it will because the leading coefficient is neg    (-x^2)


The axis of symmetry for a parabola, concave up or down, is half way between the two x intercepts 



The equation of the axis of symmetry is x = -1.5



To find the vertex, substitute x=-1.5 into the formula to find the y value.




And as catmg already suggested, use  Desmos to graph it.  wink



 Apr 24, 2021
edited by Melody  Apr 24, 2021

This was a great explanation! Your explanation and catmg's explanations help immensely, thank you!

Corduroy  Apr 24, 2021

Thanks Corderoy,  I am glad I could help.

Melody  Apr 25, 2021

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