# trig

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!

1. 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)

posted by bobpursley
2. prove that tan20 tan30 tan40 = tan 10

posted by mostafa

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