Question

If the 10th term &20th term of an A. P are (-9) &(-29) respectively. Find 15th term

Answer 1

Answer:

hope it helps.

Step-by-step explanation:

$a \: 10 = ( - 9) \\ a \: 20 = - 29 \\ = > a \: 10 = a + (n - 1)d \\ = a + (10 - 1)d \\ = a + 9d \\ = > a \: 20 = a + (n - 1)d$

$= a + ( \: 20 - 1)d \\ = a + 19d \\ subtracting \: 1 \: from \: 2 \\ a + 19d \\ a + 9d \\ = 10d = d = 10$

$a \: 15 \: \: = a \: + (n - 1)d \\ = a + (15 \: - 1)10 \\ = a + 14 \times 10 \\ = a + 140 = a = 140$