Maths Question Help! (1 Viewer)

[Bells88]

I was doing '08 Maths paper, and when marking I got a shock to see that I had got Q1a wrong! I can see where they get there answer, but somehow fail to see where I am wrong.

The question was: Evaluate 2cos(pi/5) correct to three significant figures [Sorry I don't know how to use Latex!]

I figured that since pi was in the question, it would be in radians, but the answer given is the solution you get when using the calculator in degrees mode.

Basically I know that radians are used when integrating/differentiating but does anyone have a way of guaranteeing when it is right to use degrees/radians?

 

[Jashua_Long]

Answer = 1.62

Either

(i) Type 2cos(pi /5) into your calculator with it in radians mode OR

(ii) Type 2cos(180/5) into your calculator with degrees mode

Both give the same (correct) answer.

 

[iBibah]

I just did it using radians and got the right answer of 1.62.

Maybe you have radians and degrees mixed up? It should have 'R' on the top row of your calculator.

 

[Sy123]

If it has a degrees sign:

i.e.




So basically if they give you the number without the degrees sign IT IS ALWAYS RADIANS
If it has the degrees sign it is always DEGREES

 

[Jashua_Long]

They would never write something like "2cos( pi/5 degrees).

 

[Sy123]

They would never write something like "2cos( pi/5 degrees).

You never know, teacher put it in a quiz of ours to test who actually knew the difference between them.

 

[Timothy6340]

yea we had a question where we had to change it to integrate then change back

 

[Bells88]

Okay, because I also got 1.62, and yet the book gave 2.00 as the answer. Thanks for your help guys, that has made it a little clearer!

 

[Keelan134]

Okay, because I also got 1.62, and yet the book gave 2.00 as the answer. Thanks for your help guys, that has made it a little clearer!

I'd use radians

 

[lgnorance]

You probably overlooked the fact that the answer you chose was meant to have a degrees symbol, but didn't actually have one.