Recently i've been struggling with exact values questions... wondering if anyone has any handy tips or anything?

The question is:-

What is the exact value of sin(4π/3)?

I realise it might be hard to put up the exact value triangles and stuff but if anyone could take me through it that'd be great thanks...

**0**

# exact values qustion...

Started by graham83, Jan 17 2011 12:01 PM

2 replies to this topic

### #1

Posted 17 January 2011 - 12:01 PM

### #2

Posted 17 January 2011 - 01:21 PM

Firstly if you look at where 4 / is on the graph you'll see that it is in the 3rd quadrant.

Now due to the symmetry of the sin graph, sin(4 /)=sin(5 /)= - sin(/)= - sin(2 /)

From your exact value triangles, the 30 60 one, you can work out that sin(60 )=sin(/) is 3/2 so therefore sin(4 /) must be - 3/2

In these sorts of questions where the angle given isn't on your normal exact value triangles, look at the graph and try to find other angles that you can use.

Hope this helps, if you have any follow up questions just post back

Now due to the symmetry of the sin graph, sin(4 /)=sin(5 /)= - sin(/)= - sin(2 /)

From your exact value triangles, the 30 60 one, you can work out that sin(60 )=sin(/) is 3/2 so therefore sin(4 /) must be - 3/2

In these sorts of questions where the angle given isn't on your normal exact value triangles, look at the graph and try to find other angles that you can use.

Hope this helps, if you have any follow up questions just post back

**=-=-=Marcus=-=-=**### #3

Posted 17 January 2011 - 01:39 PM

Marcus, on 17 January 2011 - 01:21 PM, said:

Firstly if you look at where 4 / is on the graph you'll see that it is in the 3rd quadrant.

Now due to the symmetry of the sin graph, sin(4 /)=sin(5 /)= - sin(/)= - sin(2 /)

From your exact value triangles, the 30 60 one, you can work out that sin(60 )=sin(/) is 3/2 so therefore sin(4 /) must be - 3/2

In these sorts of questions where the angle given isn't on your normal exact value triangles, look at the graph and try to find other angles that you can use.

Hope this helps, if you have any follow up questions just post back

Now due to the symmetry of the sin graph, sin(4 /)=sin(5 /)= - sin(/)= - sin(2 /)

From your exact value triangles, the 30 60 one, you can work out that sin(60 )=sin(/) is 3/2 so therefore sin(4 /) must be - 3/2

In these sorts of questions where the angle given isn't on your normal exact value triangles, look at the graph and try to find other angles that you can use.

Hope this helps, if you have any follow up questions just post back

Great help thanks. Glad i've signed up to the site with help like that at hand.

Thanks again

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