Question

21 If the first term of an arithmetic series is 16 and the sum of the first fifteen terms is 870,find the common difference.​

Answer 1

Answer:

common difference = 6

Step-by-step explanation:

first term of AP = a = 16

Sum of first fifteen terms = 870

$870 = \frac{15}{2} (2(16) + (15 - 1)d) \\ 870 = \frac{15}{2} (32 + 14d) \\ 870 \times \frac{2}{15} = 32 + 14d \\ 58 \times 2 = 32 + 14d \\ 116 = 32 + 14d \\ 116 - 32 = 14d \\ 14d = 84 \\ d = \frac{84}{14} \\ d = 6$

hope you get your answer

Answer 2

answer is so simple