So to solve a quadratic function, you first make the function into a quadratic equation, which is:
ax^2 +bx + c = 0
From there, you must apply the equation into the quadratic formula, which is the picture I attached (I feel like it might’ve been too confusing to try to type it out).
For example, lets say my equation was:
5x^2 + 4x - 1 = 0
My quadratic formula would then look like:
x = [ -(4) + or - √(4^2 - 4 x 5 x - 1)] / 2(5)
Fast forward through the work, it would be:
x = (-4 + or - 6)/10
x = (-4 + 6)/10 = 2/10 = 1/5
or x = (-4 - 6)/10 = -10/10 = -1
So my values for x are 1/5 or -1
So hopefully you now understand how the quadratic formula works.
So, now lets have a = 0 in my equation instead:
0x^2 + 4x - 1 = 0
x = [ -(4) + or - √(4^2 - 4 x 0 x - 1)] / 2(0)
Fast forward:
x = (-4 + or - 4)/ 0
x = (-4 + 4)/0 = 0/0 = 0
or x = (-4 - 4)/0 = -8/0 = undefined
A real number divided by 0 equals a non real number, so there’s no solution.
Long story short: A cannot equal 0 in a quadratic function, because the solution will be undefined.