# Root

• Jul 28th 2012, 11:19 AM
mariusg
Root
Ok, I just discovered that I am not allowed to use a calculator on my exam.

Now, I have no idea how to calculate roots and sin and cos values manually. And my textbook does not say.

So. If I am left with this:

Cos-1(-4/(sqrt(11)sqrt(14))) how can I solve this?

(I understand that this is not a place to provide a complete explanation so a hint to what I can google for or a website link will be enough to get me started)

Any help is appreciated.
I tried to google a little for myself but I did not find a relatively simple explanation)
• Jul 28th 2012, 11:59 AM
HallsofIvy
Re: Root
Quote:

Originally Posted by mariusg
Ok, I just discovered that I am not allowed to use a calculator on my exam.

Now, I have no idea how to calculate roots and sin and cos values manually. And my textbook does not say.

You don't! There are ways to find those "manually" but they very complicated, tedious, and subject to errror. Even in the years "BC" (before calculators) we did not do those (except possibly square roots), we looked values up in tables. I recommend you talk to your teacher, or whoever is in charge of the exam, about this.

Quote:

So. If I am left with this:

Cos-1(-4/(sqrt(11)sqrt(14))) how can I solve this?
You don't! Not by hand. There are a few "special cases" you could be expected to know, such as $sin(\pi/3)=\frac{\sqrt{3}}{2}$ or $cos(\pi/4)= \frac{\sqrt{2}}{2}$ but it would not be reasonable to expect a person to do that by hand in any restricted time. I recommend, again, that you talk with whomever is in charge about exactly what you will be expected to do on this exam. Perhaps they are planning to give you the values you need. Often, part of the test will be "without calculators" and part "with calculators"..

Quote:

(I understand that this is not a place to provide a complete explanation so a hint to what I can google for or a website link will be enough to get me started)

Any help is appreciated.
I tried to google a little for myself but I did not find a relatively simple explanation)
That's because there is NO "relatively simple explanation"!