This question came up in my math test and I don't know how to solve it! Please help!

For the quadratic equation, x^2 - 4x + c = 0 where the equation has only one solution... Find the value of c.

Question

This question came up in my math test and I don't know how to solve it!  Please help!

For the quadratic equation, x^2 - 4x + c = 0 where the equation has only one solution... Find the value of c.

unklerhaukus · Answer

$$ax^2+bx+c=0$$$$x=\frac{-b\pm\sqrt{b^2-4ac}}{2a}$$

$$x=\frac{4\pm\sqrt{16-4c}}{2}$$$$x=2\pm\sqrt{4-c}$$

anonymous · Answer

Ok

unklerhaukus · Answer

there will be only one solution when $x=2\pm0$

anonymous · Answer

Alright I get it thanks

hero · Answer

A quadratic equation will have one solution when when and only when the discriminant equals zero. Therefore

$b^2 - 4ac = 0$

a = 1
b = -4
c = c

$(-4)^2 - 4(1)c = 0 \ 16 - 4c = 0 \ 16 = 4c \ c = 4$

hero · Answer

@jadecat