Upper sec Emaths prob

Jundead SG

Hi, I have encounter such problem while doing the TYS. I have found similar topic in this forum, but the thread has expired.

The link is http://politics.sgforums.com/forums/2297/topics/331571

Does anyone know how to solve part j with respect to the question from the link?

Many thks!

eagle SG

Hi,

Set x² - x - 5 = 1/x

Rearrange and you will get

x³ - x² - 5x = 1

x³ - x² - 5x - 1 = 0

That is your cubic equation.

Do continue to ask if you are still unsure. :)

Jundead SG

Thks eagle for the solution.

But can you explain why u set the two eqns equal to one another?

Forbiddensinner SG

Thks eagle for the solution.

But can you explain why u set the two eqns equal to one another?

At the intersections, the y-values will be the same, so you can equate the equations to each other. Solving the new equation will give you the x-value of the intersections, but that is not what we want to do here.

Bluehawk156 SG

what happened to the 1?

Using your equation, x²- x - 5 = 1/x

you're supposed to get x³ - x² - 5x-1 = 0

I mean like aren't you multiplying both sides by x?

wee_ws SG

Hi Bluehawk156,

Yes, you are correct. Thanks.

Cheers,
Wen Shih

eagle SG

Yup, the 1 should be there. My bad.

Changed it. Thanks.