x^2=4x+45

Question

x^2=4x+45

anonymous · Answer

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anonymous · Answer

lilysue, giving answers straightaway is useless... instead try to show how to solve the problem without giving the answer

kinggeorge · Answer

First, you'll need to move all your x-terms to one side, so that it's equal to 0$$x^2-4x-9=0$$

kinggeorge · Answer

I should have written $-45$ instead of $-9$.

Now to factor, you need to find two numbers a, b such that $a\cdot b=-45$ and $a+b=-4$.

kinggeorge · Answer

Fortunately, these a, b are rather easy to find, as $a=5$, $b=-9$. This means that we can factor the expression $$x^2-4x-45=0$$$$(x+5)(x-9)=0$$

anonymous · Answer

x^2=4x+45
x^2-4x=45
x^2-4x+4=45+4
(x-2)^2=49
x-2=7 or x-2=-7
x1=9,x2=-5
so i'm sorry ! i write too quick ,and i made a big mistake ! 
SORRY

kinggeorge · Answer

This means that either $$x+5=0$$or$$x-9=0$$If you solve both of these equations, you get that $$x=-5$$$$x=9$$are the two solutions.

anonymous · Answer

Thank you so much for helping me with this!  I am really struggling with math.. :(

anonymous · Answer

KingGeorge's answer is another way !
it is more useful when you can get real number !But when you get the complex number my way will more useful!
Just in my opinion

kinggeorge · Answer

You're welcome. Also, the method lilysue used is called completing the square, and can be used to derive the quadratic formula. It's slightly more complex, and always gets your solutions. 

However, for a problem like this, I prefer direct factoring.