+130511 We can do this one by process of elimination.
Add all the coefficents of each polynomial together....eliminate any whose sum is not 6.
This ....A and D can be eliminated (do you see why this is true??)
So the choice comes down to B or C
Note that when we put 7 into B, that the first term is a relatively larger positive to the second term's negative and the same is true of the third and 4th terms.....thus f(7) would be positive. But our f(7) has a negative value (-54).
Thus....C must be the correct answer.....
Here's the graph.......https://www.desmos.com/calculator/jsbsapxr1a
+130511 This is due to the fact that the volume of a pyramidal object is always 1/3 that of its associated prismatic object (an object on the same base with the same height). So, the volume of a cone is 1/3 of that of its associated cylinder.
Here's the proof from Euclid's Elements......http://aleph0.clarku.edu/~djoyce/java/elements/bookXII/propXII10.html
Warning......it's a little difficult !!!!
