The sum of the first six term of an Ap is 72 and the second term is seven times th fifth term. Find the first term and common diff. And sum of the first ten terms.

Answer 1

(6/2)(2a + 5d ) = 72
6a + 15d = 72 or
2a + 5d = 24
" the second term is seven times th fifth term"
----> a + d = 7(a+4d)
6a + 27d = 0
2a + 9d = 0

subtract: 4d = -24
d = -6
then from 2a + 9d = 0, a = 27

now use your formulas to find the sum of 10 terms