## A Calculator

LailaB
Posts: 2
Joined: Thu Nov 03, 2016 3:37 pm

### A Calculator

Hello Everyone!

Is it allowed to have a calculator in the exam? What kind?

Another question is: Is there a way to calculate the sin, tan, and cos manually and without a calculator?

Qwaps
Posts: 36
Joined: Mon Mar 14, 2016 9:21 am

### Re: A Calculator

Calculator isn't allowed. The simple/known sines and cosines aside, you can usually just draw a triangle.

throwawayhehexD
Posts: 8
Joined: Sun Nov 06, 2016 12:06 pm

### Re: A Calculator

^ As mentioned, you can't use a calculator.

You won't need one, but you will need to be good at getting approximate answers. If you need exact numbers the numbers will be specifically engineered to be easy to do, like the special relativity questions usually give "nice" numbers like .6 or .8 or stuff like that.

An example of what you should be able to reason is such: when I took the October 29 GRE there was a problem where I got the answer as (7/5)^(2/3). The actual number (7/5)^(2/3) = 1.25146....etc but that doesn't matter. I remember the options being something like
(A) 1.25
(B) 1.4
(C) 1.7
(D) ??
(E) ??

I don't remember the exact options/order, but just that all the other options were numbers greater than 1.4. Now, you know that 7/5=1.4 so (7/5)^(x) where 0<x<1 has to be less than 1.4.....so clearly the answer was 1.25.

So with the actual numbers they gave you (5 and 7) and some physics knowledge you get (7/5)^(2/3) and just gotta realize that the only option is (A).

Similarly, I remember getting stuff like JUNK/(3pi) so you just gotta know that 3pi~9 or 3pi~10 (see which estimate will make your divisions easier) so that you can actually work through the junk and figure out what ~ your answer is, and you'll get the answer that way.
Last edited by throwawayhehexD on Mon Nov 28, 2016 7:50 pm, edited 3 times in total.

tooterfish
Posts: 16
Joined: Mon May 16, 2016 12:05 am

### Re: A Calculator

Agreed, it's all about making quick and accurate approximations. You ought to know the Taylor expansions for sinx, cosx, e^x as well as the binomial approximation. But really, most questions don't require that sort of math.

You should know how to estimate some common figures. For example, sqrt2 = 1.4, sqrt3=1.7, ln2 = 0.7.

The example given by throwaway, could be done like:

(7/5)^(2/3) = (49/25)^(1/3) = 2^(1/3) < 2^(1/2)

So 2^(1/3) < 1.4

Just do a bunch of practice problems, and it will become evident what sort of numerical approximations are expected. If a problem seems too mathematically technical, you've either missed the intended approach or are being far too accurate!