Stuck On An Integral: (9-3x)^3 - Help!

In summary, the conversation is about simplifying (9-3x)^3 in the context of doing an integral for Calculus 3. The person suggests using u=9-3x and du=-3dx to simplify the expression. Another person realizes they were not clear with their question and clarifies that they are not actually taking the integral, but just simplifying the expression as part of a longer answer. The second person confirms that the expansion of (a+b)^3 is a^3 + 3a^2b + 3ab^2 + b^3.
  • #1
ns5032
28
0
In the middle of doing an integral for Calc 3, and I came across (9-3x)^3, and completely forgot how to do this from algebra! Help!
 
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  • #2
Use u=9-3x
du=-3 dx so that -du/3 = dx

so you must really integrate

[tex]\int \frac{-1}{3}u^3 du[/tex]
 
  • #3
Oh, I guess I didn't phrase my question right, huh? Haha. I'm doing an integral, yes, but I'm not actually taking the integral of that... I just need to simply that part of a loooong answer I got inside an integral... if that makes sense. Just algebra stuff.
 
  • #4
Is this what it is:

(a + b)^3 = a3 + 3a^2b + 3ab^2 + b^3

?
 
  • #5
yes that is the expansion of (a+b)^3
 

FAQ: Stuck On An Integral: (9-3x)^3 - Help!

What does "Stuck On An Integral: (9-3x)^3 - Help!" mean?

This phrase refers to a mathematical equation involving an integral (essentially a fancy way of saying a type of mathematical calculation) with the expression (9-3x)^3.

What is an integral?

An integral is a mathematical operation that represents the area under a curve on a graph. It is often used to solve problems related to rates of change.

What is the purpose of the "Help!" part of the phrase?

The "Help!" part indicates that the person asking the question is struggling with the equation and is seeking assistance or guidance.

How do I solve this integral?

Unfortunately, I cannot provide a definitive answer to this question without more context and information. Depending on the specific problem and techniques used, the approach to solving this integral may vary.

Are there any tips for solving this type of integral?

Yes, there are several techniques and strategies that can be helpful when solving integral problems. Some common methods include substitution, integration by parts, and trigonometric substitution. It may also be helpful to review any relevant formulas and practice with similar problems.

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