Question 754654
To find the x intercepts you must factorise
your equation  2x^2 - 8x - 42
To make it easier take 2 out of the equation
             2(x^2 - 4x - 21)
             2(x - 7)(x + 3)= 0

Therefore x - 7 = 0
              x = 7
          x + 3 = 0
              x = -3
Intercepts are (-3,0) and (7,0)
and its vertex will be (2, -50)

Hope this helps
:-)