Is this triangle not similar because it only has two proportional sides?

The triangles are similar.

Step-by-step explanation:

They share a common angle (∠S) and the ratio of the two sides is the same, i.e. SP/SQ = SR/ST

hope it you

step-by-step explanation:

sin(7pi/6 - pi/3)  

= sin(7pi/6 - 2pi/6)  

= sin(5pi/6)  

= sin(pi - pi/6)  

= sin(pi/6)  

= 1/2  

sin 7pi/6 - sin pi/3  

= sin (pi + pi/6) - sin pi/3  

= -sin pi/6 - sin pi/3  

= -1/2 - sqrt(3)/2  

= -(1+sqrt(3))2