Given that x is measured in radians and x>20, find the smallest value of x such that

http://i37.tinypic.com/2uzs4s6.gif

Is this an inequality question?

Can someone please guide me how should I start with

Thanks!!

Printable View

- Oct 9th 2008, 03:21 AMNyRychVantelPlease help me with this GCSE trigo question
Given that x is measured in radians and x>20, find the smallest value of x such that

http://i37.tinypic.com/2uzs4s6.gif

Is this an inequality question?

Can someone please guide me how should I start with

Thanks!! - Oct 9th 2008, 04:05 AMmr fantastic
General solution:

$\displaystyle \cos \left( \frac{x - 1}{3} \right) = - \frac{\sqrt{5}}{4}$

$\displaystyle \Rightarrow \frac{x - 1}{3} = \cos^{-1} \left( - \frac{\sqrt{5}}{4}\right) + 2 n \pi$ or $\displaystyle \frac{x - 1}{3} = \pi + \cos^{-1} \left(\frac{\sqrt{5}}{4}\right) + 2 n \pi$ where n is an integer.

You want the smallest solution for x that is larger than 20.

Of course, if you have access to the appropriate technology you could always use a graph to get the answer ....... - Oct 9th 2008, 05:00 AMNyRychVantel
Please correct me if I'm wrong.

http://i34.tinypic.com/2na4mme.jpg - Oct 9th 2008, 02:17 PMmr fantastic