Question #573d2

1 Answer
Sep 21, 2016

#(3-sqrt(3))/6#

Explanation:

In the given trigonometric expression first we must light on some formulas included :

#cos((5pi)/6)=cos(pi-(pi/6))#
And we know that
#cos(pi-alpha)=-cos(alpha)#
So,
#color(blue)(cos((5pi)/6)=cos(pi-pi/6)= -cos(pi/6)=-sqrt(3)/2#

Now we have:
#tan((7pi)/6)=tan(pi+pi/6)=tan(pi/6)#
Knowing the formula that says:
#tan(pi+alpha)=tan(alpha)#
We have:
#color(red)(tan((7pi)/6)=tan(pi/6)=sqrt(3)/3)#

Let's substitute the answers in the expression given above:
#sin(pi/6)+cos((5pi)/6)+tan((7pi)/6)#
#=1/2+color(blue)(-sqrt(3)/2)+color(red)(sqrt(3)/3)#
#=(3-sqrt(3))/6#