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Aug 4, 2015
 #1
avatar+130511 
+15

I possibly don't understand this, but I think you want to find the values where the differences in the height of the curves is more than 4 but less than 7....so we have....

 

[(1/2)x^2 + 7] - [(-1/4)x^2 + 3x] > 4   simplify

 

(3/4)x^2 - 3x + 7 > 4

 

(3/4)x^2 - 3x  + 3  > 0      and this is > 0 everywhere except  at x = 2 → ( -∞, 2) U (2, ∞)

 

See the graph, here....https://www.desmos.com/calculator/komufu5yah

 

And we also have

 

[(1/2)x^2 + 7] - [(-1/4)x^2 + 3x] < 7   simplify

 

(3/4)x^2 -3x  + 7 < 7 

 

(3/4)x^2 - 3x < 0        and the interval where this happens is (0, 4)

 

See the graph here.....https://www.desmos.com/calculator/eepspvllj9

 

Now......only the intersection of these intervals will  satisfy this inequality.......these will be (0, 2) and (2, 4)

 

Note that when x = 2....the difference in the height of the curves is just 4......we need it larger than 4, though

 

See the graph here....https://www.desmos.com/calculator/hpb4r3uo1m

 

This one was a little tricky....I hope I haven't missed anything !!!

 

 

  

Aug 4, 2015

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