6x^2 -14x = 0 , using factoring method.

Take out the highest common factor.

The highest common factor between 6 (which 2*3) and 14 (which 2*7) is 2

The highest common factor between x^2 (which is x * x) and x(which is x) is x.

2x(3x - 7) = 0

Now either 2x = 0 in which case x = 0
or
3x - 7 = 0
3x = 7
x = 7/3 

The graph below shows you the answers to where 6x^2 - 14x cuts the x axis is below.

Opposite angles in a cyclic quadrilateral add up to 180°