Question

Find the 7th term of the arithmetic sequence 4x + 5, 11x + 9,18x + 13, ...

Answer 1

Explanation:

we see the common difference is

a2-a1 = 11x + 9 - 4x - 5 = 7x + 4

an = an-1 + (7x+4) = a1 + (n-1)×(7x+4)

for a7 we have then

a7 = 4x + 5 + 6×(7x +4) = 4x + 5 + 42x + 24 = 46x + 29