Thread: Algebra and Surds!

Find the exact value of

x² + 1/x²

if x = 1 + 2 * square root of 3 / 1 - 2 * square root of 3

Answer: 434/121 = 3 71/121

Does anyone end up with this answer?? Pls help! I dnt kno whether it's a printing error in the textbook or I just cnt solve it

Originally Posted by Mirage

Does anyone end up with this answer?? Pls help! I dnt kno whether it's a printing error in the textbook or I just cnt solve it

Answer: 434/121 = 3 71/121

Your answer is correct!

Thanks for your response

I don't know how to arrive at that answer. Would you be able to type out your working out pls?

Would be more helpful if you used some brackets, is this the question? find $\displaystyle \frac{x^2+1}{x^2}$ where $\displaystyle x = \frac{1+2\sqrt{3}}{1-2\sqrt{3}}$

It is x² + (1/x²)
second part is correct

Sorry, I'm new to this. How do you type maths? Is there some sort of program that you use?

Originally Posted by Mirage

Sorry, I'm new to this. How do you type maths? Is there some sort of program that you use?

Have a quick read of this. http://www.mathhelpforum.com/math-he...orial-266.html

Originally Posted by Mirage

It is x² + (1/x²)

$\displaystyle (\frac{1+2\sqrt{3}}{1-2\sqrt{3}})^2+\frac{1}{(\frac{1+2\sqrt{3}}{1-2\sqrt{3}})^2}$

Start expanding brackets.

You also can find x+1/x=2cos(t) (much easier )

and then x^2+(1/x^2)=2cos(2t)

Originally Posted by Also sprach Zarathustra

You also can find x+1/x=2cos(t) (much easier )

and then x^2+(1/x^2)=2cos(2t)

Good advice ASZ, although remember this is in a pre-uni level forum.