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The measure of an angle formed by two lines that intersect outside a circle is half the difference of the measures of the intercepted arcs.
81
Consider the given diagram.
We want to find m∠A. We know that if two lines intersect outside a circle, the measure of the angle formed by the intersection of the lines is half the difference of the measures of the intercepted arcs.
Now, we can substitute mBDC and mCB in the expression for m∠A and simplify.
mBDC= 261, mCB= 99
Subtract term
a/c* b = a* b/c
Multiply
Calculate quotient