Hi there...Originally Posted by Confuzzled?
For Qn 1, for typing easeness, i will denote the Sigma sign n on the top, 1 underneath as (S1).
= (S1) (2r) - (s1) (7)
= 2 (S1)(r) -7n
=2 (1/2)(n)(n+1) - 7n
=n2 + n - 7n
=n2 - 6n
For Qn 2, 1st term = a = 14 ; Sn = d = -6
Sn = n/2(2a + (n-1)d) => eq 1
Substitute the following values on top into eq 1 and solve for n.
For Qn 3,
1st Term = 2x + 1
2nd Term = 3x + 2
3rd Term = 5x - 1
As they are in arithmetic series, they will have a common difference.
(3x + 2) - (2x + 1) = (5x - 1) - (3x + 2)
Solve the above equation for x.
Hope these can be of some help to u.