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  20

Step-by-step explanation:

The average term in the series is the average of the first and last terms:

  average term = (25 +101)/2 = 126/2 = 63

The sum of the series is the product of the average term and the number of terms:

  Sn = n(average term)

  1260 = 63n

  1260/63 = n = 20

The number of terms in the series is 20.

∠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°

(-1,-0.5)

step-by-step explanation: