Assume that lines that appear tangent are tangent. find the value of the variables a. a = 90; b = 90; c = 70; d = 65 b. a = 90; b = 84; c = 64; d = 60 c. a = 84; b = 90; c = 68; d = 65 d. a = 86; b = 88; c = 70; d = 62

B is an inscribed angle and an inscribed angle is half the measure of its intercepted are, and likewise, the intercepted arc is double the angle, so b = 90. a is a central angle which has the same measure as its intercepted arc.  So a = 90.  the measure of c is half of its intercepted arc, which is 140, so c = 70.  The outside measure of a circle is 360, and we have the measure of 2/3 of it so we can figure out the measure of the arc that is intercepted by angle d. 360-140-90=130.  Half of 130 is 65.  a = 90, b = 90, c = 70, d = 65. A from above.