Question

How to solve a quadratic equation when c=0

Answer 1

Lets say we have a quadratic equation:

3x^2 + x + 0 = 0

Now, since if we add or subtract 0 from something, the original value stays the same, which means we can write the equation as 3x^2 + x = 0 and ignore the “+0”.

In these kinds of equations, you /can/ use the quadratic formula, but theres a much quicker way. If we factor 3x^2 + x, we get x(3x + 1) = 0. Here, x has two possible values — since the result of the multiplication is 0, that means that either one expression or the other must equal 0. In essence:

If x(3x+1) = 0 then x = 0 or 3x+1 = 0
One of the solutions is that x = 0. Lets find the other.

3x+1=0
3x= -1
x = -1/3

So x1 = 0 and x2 = -1/3. So basically you solve these equations using basic factorization. :)