Question 1132681

The first term of an arithmetic progression is -8.The ratio of the 7th term to the 9th is 5:8. Calculate the common difference 
<pre>{{{matrix(1,6, a[1], "=", - 8, ",", so, matrix(2,3, a[7], "=", - 8 + 6d, a[9], "=", - 8 + 8d))}}}
We then get: {{{matrix(1,3, (- 8 + 6d)/(- 8 + 8d), "=", 5/8)}}}
8(- 8 + 6d) = 5(- 8 + 8d) ------- Cross-multiplying
- 64 + 48d = - 40 + 40d
48d - 40d = - 40 + 64
8d = 24
d, or common difference = {{{highlight_green(matrix(1,3, 24/8, "=", 3))}}}