Turning points

yhpigs

New member
Joined
Aug 12, 2018
Messages
8
Hello everyone!

The equation that I'm sketching a graph for is: y = (x+3)(x+2)(x-1) at -4.5 ≤ x ≤ 4.5

I've already found x and y intercepts, and derived the equation (y' = 3x^2 + 8x + 1)

I've used the quadratic formula to find the x-values of the original equations turning points, but the y-values are where I'm getting stuck.

I originally subbed in the x-values into the derived equation, but when I check my answers against the turning point co-ordinates on my graphics calculator, they're not even close.


This is my working for the x-values:
Screen Shot 2018-08-18 at 7.39.01 pm.jpg

These are my answers for the y-values when subbing in each x-value:
Capture 3.png


...and these are the co-ordinates for the turning points:
Capture 2.pngCapture 1.png


So I've got the x-values right, but I have no idea how to find the y-values now.

What am I doing wrong?
 
… These are my answers for the y-values when subbing in each [critical] value … What am I doing wrong?
You substituted the critical values into y' instead of y.


… I've used the quadratic formula to find the [critical] values …
Your work looks good, but you could simplify further.

The radicand (52) is 4∙13, so you have √4 ∙ √13 to simplify. After that, factor 2 from the numerator, and then make a cancellation with the denominator.

You also rounded to two places incorrectly, on your -2.53 ;)
 
Top