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1. Let's just pretend for the moment that c3+4c>5c2 is an equation, so the equation would be c3+4c=5c2. Let's solve this as if it were a regular equation. 

 

c3+4c=5c2Subtract 5c^2 from both sides so that every term containing a "c" is on the left. 
c35c2+4c=0Factor out the GCF of the left-hand-side of the equation, c.
c(c25c+4)=0Now, let's factor some more. The trinomial is factorable. 
c(c4)(c1)=0Now, let's solve for all the possible values of "c."
c1=0c2=1c3=4 
  

 

 

Therefore, we have defined many possible ranges where the solutions of this inequality can lie. We will have to test all of them. The ranges are as follows:

 

c<00<c<10<c<4c>4

 

Now, let's test values in these ranges. 

 

For the range c<0, let's test a point in this range, say -1, and see if it satisfies the original equation.

 

c3+4c>5c2Plug in -1 as a test point and see if it satisfies.
(1)3+41>5(1)2If you use some logic here, you will realize that this test point does not satisfy the original inequality. (-1)^3 and 4*-1 are both negative values, so adding them together will result in a negative value, too. On the right hand side, we have a number squared, which will always be positive. Multiplying this result by 5 does not affect the signage. Therefore, the right hand side cannot be greater than the left, so it is a false statement.
(1)3+415(1)2This means that any numbers in the range c<0 are not solutions to the original inequality.

 

Now, let's try the range \(0 . I will choose 1/2.

 

c3+4c>5c2Plug in the desired point.
(12)3+412>5(12)2This one does not appear to be as clear-cut, so we will have to perform more simplification.
18+2>54Here, you can stop. 2 is already greater than 5/4.
 This means that any real number in the range \(0  is a solution to the original inequality.

 

Now, let's try the terciary range of \(1 . My test point, in this case, will be 2. Always pick a point that is easiest to plug in. Overcomplicating matters is only a burden to yourself.

 

c3+4c>5c2Evaluate if true when c=2.
23+42>522This one appears to require some more iterations to determine. 
8+8>20I think it is obvious at this point that this is untrue. 
8+820As aforementioned, \(1  is not in the range. 
  

 

And finally, c>4 is the last one. Let's do the next integer, c=5. 

 

53+52>5152You can use any tricks you desire to evaluate these inequalities quicker. Here is the one that I noticed straightaway.
53+52=53Well, there is a 5^3 on both sides of the inequality. On the left, a 5*2 remains, so the left side has to larger. Notice how I refrained from actually evaluating this completely as to preserve precious time.
 c>4 is the range as well.

 

Consolidating all this information, we can conclude that \(0  or  c>4. When you convert to inequality notation, you get  (0,1)(4,+)

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Feb 27, 2018
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Feb 27, 2018
Feb 26, 2018
 #1
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Feb 26, 2018

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