Solve[x^2 - 3*x - 4 == 0, x]

x /. Solve[x^2 - 3*x - 4 == 0, x]

Clear[sol]

sol := Solve[x^2 - 3*x - 4 == 0, x]

x /. sol

x^2 - 3*x - 4 /. sol

Solve[{2*x + y - 2 == 0, x - y - 1 == 0}, {x, 
        y}]

{x, y} /. 
      Solve[{2*x + y - 2 == 0, x - y - 1 == 0}, {x, 
          y}]

Solve[{x - 2*y + 3*z == 2, 
        2*x - 3*y + 4*z == 
          3, 
3*x - 8*y + 13*z == 8}, {x, y, 
        z}]

Clear[sol2]

sol2 := 
      Solve[{x - 2*y + 3*z == 2, 
          2*x - 3*y + 4*z == 
            3, 
3*x - 8*y + 13*z == 8}, {x, y, 
          z}]

sol2 /. z -> c

Solve[{x - y - 2 == 0, x - y - 1 == 0}, {x, y}]

Plot[Log[x + 2] - Log[x] - 3, {x, 0.01, 3}]

FindRoot[Log[x + 2] - Log[x] == 3, {x, 1}]

NSolve[Log[x + 2] - Log[x] == 3, x]