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1. How do you find the solution to x^3-27x-90=0.Thanks for the help in advance.

2. Use this formula where a=1, b=0, c=-27 and d=-90
3. (Original post by xpointx)
How do you find the solution to x^3-27x-90=0.Thanks for the help in advance.
If this is A-level, then only graphically or numerically
However there is a method which leads to the solution of being given by
then solution of equation is u+v
4. (Original post by xpointx)
How do you find the solution to x^3-27x-90=0.Thanks for the help in advance.
Is this for FP1?

You can expand the equation:

And compare it to your cubic to work out the values of

That should give you the roots with a bit of manipulation I would think.
5. x^3 - 27x - 90 = 0

x^3 - 27x = 90

x ( x^2 - 27) = 90

x ( x^2 - x^3 ) = 90

:. x ( x - 3 ) ( x - 3 ) = 90

So the solutions you can work out.

x=90
x=93

Working

x - 3 = 90
:. x= 90+3
x=93
6. (Original post by Sena5)
x^3 - 27x - 90 = 0

x^3 - 27x = 90

x ( x^2 - 27) = 90

x ( x^2 - x^3 ) = 90

:. x ( x - 3 ) ( x - 3 ) = 90

So the solutions you can work out.

x=90
x=93

Working

x - 3 = 90
:. x= 90+3
x=93
You've made quite a few mistakes here:

First you changed 27 to x^3 which isn't correct.

Then you said x^2 - x^3 = (x-3)(x-3) which is also wrong.

Then you read off solutions to x ( x - 3 ) ( x - 3 ) = 90 but forgot that the right-hand-side is not 0.

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