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avatar+118723 
+10

I would consider the graph

y=(x+3)(2x-1)(2-x)    

The roots are  -3, 1/2, and 2

 

It is of the form    

 

 $$\\y=-ax^3+bx^2+cx+d\\\\
$Where a,b,c and d are real numbers and a is positive.$$$

 

****    I instantly know the shape of this graph.    ****

 

Refer to this post that I did in the past to understand what I mean.

It will help you enormously if you understand this older post  !!!

http://web2.0calc.com/questions/how-do-you-find-a-power-function-that-is-graphed

 

Here is the graph.  I have hidden the y axis because it is not relevant.

you do not need a graphing calc to get this basic shape.  It is easy to draw freehand.

The answer is all the x values where the graph is ABOVE the x axis.  It is that easy!

You do not need to test any points!

 

Solutions    $$(-\infty,-3)\;\;and\;\;(0.5,2)$$

 

If you have any questions please ask.    

If you fully understand this you will be a step in front of many others :)

Apr 16, 2015

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