An arithmetic progression start 3+2a, 3+4a,3+6a if the fifth term is 73 work out value a?
first term is 3+2a
common difference = d = 3+4a - (3+2a) = 2a
term(5) = first term +4d
= 3+2a + 4(2a) = 73
10a = 70
a = 7
check:
d = 14
terms are: 17, 31, 45, 59, 73
all looks good