Triangle bcd is isosceles and line bc is congruent to line bd. what is the measure of arc bc?

arc BC is 130º

Step-by-step 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

12r - 8 - 12

you have to combine like terms. below i have bolded the like terms:

12r - 8 - 12

together it combines to:

12r - 20

hope this !