Equation in x

• Apr 21st 2010, 03:23 AM
Stuck Man
Equation in x
I need help with b(i). Am I supposed to have an equation starting with x= ?

I have written:

9000x=96000+6x^3

x^3-1400x+15000=0
• Apr 21st 2010, 03:42 AM
undefined
Quote:

Originally Posted by Stuck Man
I need help with b(i). Am I supposed to have an equation starting with x= ?

I have written:

9000x=96000+6x^3

x^3-1400x+15000=0

b(i) doesn't say solve for x, just write an equation. All you have to do is write S(x) = 9000.

(Replace S(x) by the expression proven in part a.)
• Apr 21st 2010, 04:04 AM
Stuck Man
Ok, thanks. I've done the next part with trial and improvement. Since the factor is an irrational number I think that would be a good choice of method?
• Apr 21st 2010, 04:23 AM
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Quote:

Originally Posted by Stuck Man
Ok, thanks. I've done the next part with trial and improvement. Since the factor is an irrational number I think that would be a good choice of method?

Yes, that method seems well suited to this problem. The reason isn't so much that the answer is irrational, but that it may be difficult to find exactly, and easier to approximate.