Which explains why the sequence 81,3,1/ is arithmetic or geometric

 It is geometric progression .

Step-by-step explanation:

Since we have given that

the sequence i.e.

where

Since it has common ratio instead of common difference ,

Hence, it is geometric progression rather than arithmetic progression.

∠acb = 8°

step-by-step explanation:

∠xba lies on the circle and is half the measure of the intercepted arc ax

hence

measure of arc ax = 2 × 42° = 84°

∠acb is outside the circle and is

∠acb = (arcab - arcax ), hence

∠acb = 0.5 (100 - 84) = 0.5 × 16° = 8°