Checking the Sine Rule
Notice how when we divide a side by the Sine of the opposite angle we get the same result for all three pairs of sides and angles. Move a point in the triangle to see how the sides and angles change but the three ratios of x/sinX always are equal.
Move a point so that one of the angles is obtuse. Does the Sine Rule still apply? What do you think this means about Sine and obtuse angles?