There are three to five kinematics equations reported, where from the first two (v=v0+at and x=x0+v0t+21at2), the third can be obtained, also the fourth and the fifth, by eliminating an unknown.
The idea of five equations is that each for one unknown, which are x−x0, v (or vt), t (or Δt, t−t0), v0, and a.
They are obtained by integration of constant acceleration a and using initial conditions for velocity v(t0)=v0 and position x(t0)=x0 with t0=0 in general, but it is common to choose t0=0.