# Put an initial condition on some parameter

Good morning, I'm new in the world of Mathematica, so I'm sorry if my question isn't very relevant. I'm trying to solve a system of 5 equations withs many parameters. To be clear, I will hit the core of my problem. Here is my code :

$Assumptions = q > 1; C1[a_, q] := -(7/5) + (7 a)/5 + 2 q; //** here a is a real number and q is a real number strictly grater than 1 Reduce[C11[a, q] <= 0, a]  The answer that I got is "q ∈ $$\mathbb{R}$$ && a <= 1/7 (7 - 10 q). This means that my code didn't take the assumption on q. Please could you propose a method to solve this issue ? Of course my system contains a lot of parameters with different constraints to be injected (bit I avoid it here) Thank you for helping • @cvgmt I want to reduce the expression with respect to a. When I wrote what you proposed, I get " q>1 is not a valid variable" – A H Jul 19, 2022 at 13:25 • You need to specify the condition inside Reduce like: Reduce[{C1[a, q] <= 0, q > 1}, a] Jul 19, 2022 at 13:31 • Clear[C1, a, q]; C1[a_, q_] = -(7/5) + (7 a)/5 + 2 q; Reduce[{C1[a, q] <= 0, q > 1}, a] Jul 19, 2022 at 13:38 • @DanielHuber @@cvgmt Thank you for your answers. With your help, I got q >1 && a <= 1/7 (7 - 10 q) – A H Jul 19, 2022 at 13:44 • Note that FreeQ[Options[Reduce], Assumptions] gives True, so of course Reduce[] is not going to be affected by setting $Assumptions. Jul 19, 2022 at 14:51