# Extremely easy math, but need expression

by Joel DB
Tags: expression, extremely, math
 P: 3 Okay, This could be the easiest math question on here... but I'm going to ask the dumb question anyway. I have several coordinate points to solve for, and in each case I subtract the same amount from the previous "x" to get the next "x" value (X2...3...4...5...). The only point where I subract a different value is X1. The rest have a constant rate of change (derivative?). Example: 1.) X1 = (some vaule) – 30’ 2.) X2 = (X1 – 60’), X3 = (X2 – 60’), X4 = (X3 – 60’), X5 = (X4 – 60’), X6 = (X5 – 60’) There has to be a simple mathematical formula, other than this sloppy one. Any help would be great.
 Mentor P: 21,019
 P: 9 like Mark44 said this is an arithmetic progression Here the difference between two terms(of the sequence) is equal Tn=a+(n-1)d where a is the first term and d is the difference between two terms(d=T2-T1)

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