equations with squares and cubes

Mariner · 2011-01-27 16:04:08

Hi, I was wondering with an equation such as this : (x^2 - 1 )^3 = 27 do I times the 3 into the brackets and cube the last term (27)?

bobbym · 2011-01-27 16:14:27

Hi Mariner;

That is what you have? To solve it you would take the cube root of both sides first:

Now you just have a quadratic to solve. Using inspection you can see that one root is x = 2. Can you get the other?

Or are you trying to expand that out?

Mariner · 2011-01-27 16:27:42

bobbym wrote:

Hi Mariner;
That is what you have? To solve it you would take the cube root of both sides first:
Now you just have a quadratic to solve. Using inspection you can see that one root is x = 2. Can you get the other?
Or are you trying to expand that out?

From the last step you have there I did:

x^2 - 1 = 3
X^2 = 3+1
X^2 = 4
x= root 4
x= 2

I know it should be 2,-2 but how do I get the negative 2?

bobbym · 2011-01-27 16:38:42

First you should know that (-2)^2 = 4 just the same as 2^2 = 4. Also I encourage people to think about that problem before running to the methods of algebra.

But to do it in a more formal way. When you got here:

Use small x for the variable x instead of the capital x.

x = 2

x = - 2

Mariner · 2011-01-27 17:21:43

excellent! thanks mate!

bobbym · 2011-01-27 17:41:33

Glad to help!

Math Is Fun Forum

#1 2011-01-27 16:04:08

equations with squares and cubes

#2 2011-01-27 16:14:27

Re: equations with squares and cubes

#3 2011-01-27 16:27:42

Re: equations with squares and cubes

#4 2011-01-27 16:38:42

Re: equations with squares and cubes

#5 2011-01-27 17:21:43

Re: equations with squares and cubes

#6 2011-01-27 17:41:33

Re: equations with squares and cubes

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