Posted by **jenny** on Thursday, August 25, 2011 at 12:46am.

Use the exact values of the sin, cos and tan of pi/3 and pi/6, and the symmetry of the graphs of sin, cos and tan, to find the exact values of sin

-pi/6, cos 5/3pi and tan 4pi/3.

I have found the answers to the first three using the special tables

sin pi/6 = cos pi/3 = 1/2

cos pi/6 = sin pi/3 = root 3/2

tan pi/3 = root 3

tan pi/6 = 1/root 3

I know that the symmetry of sin(-pi/6 is in the third quadrant, so 7pi/6 =

- 0.5

the symmetry of cos 5pi/3 i have taken 2pi - 5pi/3 to give cos pi/3 = 0.5 but i am not too sure where the symmetry comes in

With the tan I do not quite know where to start. Maybe pi + pi/3.

As for plotting the graphs of sin,cos and tan; I do not know where to start here using the pi radians (whereas as usually I am good at plotting graphs. (perhaps it is an age thing :-(

- math -
**Damon**, Thursday, August 25, 2011 at 4:50am
tan 4 pi/3 is in quadrant three pi/3 or 60 degrees below the -x axis

so

both x and y are negative

tan (pi+pi/3) = tan (60 deg) = sqrt(3)

- math -
**jenny**, Thursday, August 25, 2011 at 6:54am
Can anyone give me some pointers on how to plot the graph in excel please

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