The first and last terms of an A.P. are -3 and 145,respectively.if the common different is 4.find the,a.12th,b.25th term,c.the number if terms in the A.P.

Answer 1

we know a and d but not the number of terms
a+(n-1)d = 145
-3 + (n-1)(4) = 145
4n - 4 = 148
4n = 152
n = 38

the rest is routine using your formulas