x is the multiplication symbol.
Your keyboard surely has a handy x key, which is used for variables.
Since there is a common difference,
(2x+1)-x = (4x+1)-(2x+1)
x = 1
That makes the sequence 1,3,5,...
so
S18 = 18/2 (2*1+17*2) = 324
The first three terms of an AP are ×, 2×+1, 4×+1, find × and the sum of the first 18 terms
1 answer
1 answer