1. The problem statement, all variables and given/known data Chemical reactions being studied in which a body A undergoes transformations according to the following scheme: http://prntscr.com/8shuvb k1, k2, k3 , k4 are the rate constants . We denote x (t ), y ( t) , z (t) the respective concentrations of the products A, B, C at a given time t ( t expressed in minutes). The initial conditions x (0) = 1, y (0) = 0 and z ( 0) = 0 . Is arranged above the vessel where the reaction takes place by a burette which is poured product A at a constant speed in the tank. Under these experimental conditions, functions x , y, z defined on the interval [0 ; + infinite [ check the following differential system : dx/dt (1-2x +y+ z) dy/dt (x - y) dz/dt (x - z) Question 1: Calculate d/dt( x + y + z) and , using the initial conditions, deduce that : y(t) + z(t) = 1 + t - x(t) Question 2: Demonstrate that x is a solution of the differential equation (E) : dx/dt + 3x = 2 + t, then resolve Equation ( E) knowing that it validates the initial condition x (0) = 1 . 2. Relevant equations 3. The attempt at a solution Question 1: dx/dt+dy/dt+dz/dt= 1-2x+y+z+x-y+x-z dx/dt+dy/dt+dz/dt= 1 integral dx/dt+ integral dy/dt+ integral dz/dt= integral ( 1 dt) x(t)+y(t)+z(t)=t*c y(t)+z(t)=t*c-x(t) Question 2: dx/dt+3x=2+t dx/dt =2+t-3x dx/dt(x) =1 1= 2+x-3x 1=2+-2x ... does not work. :( I am not sure what to do here, some tips would help.