Xn = a + (n-1)d
X5 = a + 4 d
X5 - 1 = 2 [ a + d ]
X10 - 3 = 2 [ a + 3 d ]
but X10 = a+9d
so
a + 4 d - 1 = 2 a + 2 d
a = 2 d - 1
a + 9 d - 3 = 2 a + 6 d
a = 3 d -3
combine
3 d - 3 = 2 d - 1
d = 4
You take it from there.
The fifth term of an A.P exceeds twice the second term by 1.The tenth term exceeds twice the fourth term by 3.
Find:1.the first term.
2.the common difference.
3.the sum of first twenty five terms.
1 answer
1 answer