Question

PLEASE HELP!!

In circle O, AC and BD are diameters.

What is mBC?


A. 50°

B. 80°

C. 100°

D.130°

Answer 1

It is D

Explanation:

Because I said so

Answer 2

D.130°

Explanation:

An arc measure ia an angle an arc makes with the circle's centre and is proportional to the angle it subtends to the circumference, arc length.

-Given that AC and BC are diameters, then
`\angle AOB =\angle DOC` since they are alternate angles.

`\angle AOB =\angle dOC=180\textdegree\\\\3x-70=x+10\\\\x=40\textdegree`

#Since angles on one side of a diameter sum up to 180°, mBC is calculated as:

`(3x-70)+m\angle BC=180\\\\M\angle BC=180+70-3* 40\\\\=130\textdegree`

Hence, mBC=130°