Solve for x: x^2=x+4

Question

anonymous · Answer

bring (x+4) to the other side and either factor or use the quadratic equation.

lgbasallote · Answer

put everything on one side first

x^2 - x - 4 = 0

now use the quadratic formula
$$\large x = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}$$
$$\large x = \frac{-(-1) \pm \sqrt{(-1)^2 - 4(1)(-4)}}{2(1)}$$
got it?

anonymous · Answer

Is there a way of knowing when you have to use the quadratic equation and when you can just factor?

lgbasallote · Answer

well i for one initially thought it can be factored but i couldnt...my point is i base my judgment on trial and error...

anonymous · Answer

Theres not really a method, you have to eyeball it. If you can't think of numbers off the top of your head or it is not obvious what the answer should be, then most likely it will be using the Quadratic Equation

lgbasallote · Answer

but if you think abt it the factors of 4 are:

4 x 1 and 2 x 2

neither factor can produce -1 when added/subtracted

anonymous · Answer

Thanks :)