3(4)= x(x-4)
12 = x² - 4x
x² - 4x - 12 =0
This is now a quadratic equation and we can solve by factorisation method
x²- 6x + 2x - 12 = 0
x(x - 6) + 2(x - 6) =0
(x-6)(x+ 2) = 0
Either x+2 = 0 or x - 6 = 0
x =-2 or x=6
There is no negative length
Hence, x =6
DC = x + x - 4
substitute x =6 in the above
DC= 6+6 - 4 = 8
