Which equation can be used to determine the reference angle, r, if 0=7pi/12?

The answer is "r=pi-theta".

The reference angle refers to the angle that the given edge or angle makes with the x-pivot.  Regardless where the angle closes or ends, it does mot matter where the terminal side of the angle is located, the reference angle measures the nearest distance of that terminal side to the x-axis.

Sorry can't answer that question

the law of definite proportions states samples of a compound will always contain the same proportion of elements by mass. in other words, a given compound will always contain the same elements in the same proportions by mass.the law of multiple proportions states when two elements combine with each other to form more than one compound, then the weights of one element that combine with a fixed weight of the other are in a ratio of small whole numbers.