Question

Triangle BCD is isosceles and line Bc is congruent to line BD. What is the measure of arc BC?

Answer 1

Since arc CD is 100 degrees, the rest of the circle must be 260 degrees.  Since the rest of the circle is made up of two equal arcs, then arc BC must be half of 260 degrees.  Thus, the answer is 130 degrees, C.

Answer 2

arc BC is 130º

Explanation:

Arc CD is 100º, we know that the whole circumference measures 360º.

We also know that same measure angles oppose to same measure sides.

Since BCD is isosceles, the 260º left of the circumference should be equally divided between the BD and BC arcs.

Therefore, each one of these arcs measure 260 / 2 = 130º

Arc BC = 130