it says solve for x. 2n^2-n-15=0

Either change the n to x or solve for n!!!

(2n+5)*(n-3) = 2n²-n-15 = 0

so n = -5 or n = 3

 

Similarly,

2x²-x-15=0 means x = -5 or x = 3

$$2n^2-n-15=0$$

You can solve this using the quadratic formula or you can factorise it manually.

I'll give you more detail on the manual method.

$$2n^2-1n-15=0$$

You need to find two numbers that multiply to -30 and add to -1Well one will be negative and the other positive. Plus they 

Well one will be negative and the other positive. -6 and +5 works

So  $$-1n$$   is replace   $$-6n+5n$$

 

$$\begin{array}{rll}
2n^2\:\:-1n\:\:-15&=&0\\
2n^2-6n+5n-15&=&0\\
2n(n-3)+5(n-3)&=&0\\
(2n+5)(n-3)&=&0\\
\end{array}$$

 

$$\begin{array}{rllrlrll}
2n+5&=&0 &\mbox{ OR }& n-3&=&0\\
2n&=&-5 &\mbox{ OR }& n&=&3\\
n&=&-2\frac{1}{2} &\mbox{ OR }& n&=&3\\
\end{array}$$

Or you can use the quadratic formula. This will help you remember it.

https://www.youtube.com/watch?v=O8ezDEk3qCg

-----------------------------------------------------------------------

\begin{array}{rllrlrll}

2n+5&=&0 &\mbox{ OR }& n-3&=&0\\

2n&=&-5 &\mbox{ OR }& n&=&3\\

n&=&-2\frac{1}{2} &\mbox{ OR }& n&=&3\\

\end{array}

 

Heurika would you give me a hand please.  (or someone else if you can)

I want the n (after the OR) up against the equal sign but I can't get it to happen.  I've tried a couple of different things but it just refuses.  Also, why arn't the mbox blank spaces in there? 

Thank you.