Hello. I'm trying something here... I created the following formula for something I'm playing with: x = ((a+9)*(a-2))/2 + b There's a catch here, the following inequality has to be valid a > b Now I'm having some trouble here... 1) Is there some way to find a and b only having the value of x and knowing that inequality is always valid? Let me elaborate more on this topic, I have a few more questions related to the same problem (even if it isn't obvious by just reading this topic, but it is all related): This is probably basic math... so please bear with me. I have the following sequence of numbers: 1 3 6 10 15... It isn't an AP because the difference isn't constant. It starts in 2, then 3, 4, 5 and so on. Changing 1 each time. 2) Is there a way to know if a number is in this sequence? For instance, is 55 in this sequence? (it is...) 3) What is the difference used to reach some number in the sequence? For instance, the number 55, what is the difference that was used to find it (it is 10, the previous number is 45).