If angle C is 85o, what is the measure of angle RDB? Include all your calculations and an explanation of how you came to your conclusion.

Question

If angle C is 85^o, what is the measure of angle RDB? Include all your calculations and an explanation of how you came to your conclusion.

Answer 1

Hi,

As you can see, < C is inscribed angle and it is front of arc BAD and relation between arc and angle is:

< C = 1/2 ( arc BAD) = 85 =====> arc BAD = 2* 85 = 170 degree

as you see <BDR is Tangent-chord angle and measure of this angle = 1/2 ( front arc) =

1/2 ( arc BAD)=1/2(170)

As a result < BDR = 85 degree

Note: you need to know 3 angles are in any circle 1- central angle 2- inscribed angle 3- tangent-chord angle

I hope it is useful,

Minoo