Posted by **Anonymous** on Thursday, November 19, 2009 at 7:38pm.

use sum or difference identities to find the exact value of the trigonometric function: tan 345

please show work, i cant figure out what im doing wrong!

- trig -
**bobpursley**, Thursday, November 19, 2009 at 8:11pm
tan(345)?

Tan(2*345)=tan(690)=tan(720-30)=tan(-30)

tan(2*345)= 2*tan(345)/(1-tan^2(345)

lets call tan(345) Y

tan(-30)=2y/(1-y^2)

Call Tan(-30) X

x-XY^2=2Y

XY^2+2Y-x=0

use the quadratic to solve for y in terms of X

(tan(-30)=-1/sqrt3)

- trig -
**mostafa**, Thursday, January 6, 2011 at 2:05pm
prove that tan20 tan30 tan40 = tan 10

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