Melody

What?

3x+4y+y+8x

If you have 3 xylophones and 4 yaks, and another xylophone and another 8 yaks 

What do you have?

The number that is in front of a letter

5x    the coefficient of x is 5

Thanks Ninja  

It is a new easier question!

Your question makes my brain hurt.    

you need to use brackets and make your meaning clear.

Are you sure that the question is correct?

$$\\\lim_{h\rightarrow0} \frac{(5+h)^{-1} -5^{-1}}{h}\\\\
=\lim_{h\rightarrow0} \frac{\frac{1}{5+h}-\frac{1}{5}}{h}\\\\
=\lim_{h\rightarrow0} \left(\frac{5}{5(5+h)}-\frac{5+h}{5(5+h)}\right)\div h\\\\
=\lim_{h\rightarrow0} \left(\frac{-h}{5(5+h)}}\right)\times \frac{1}{h}\\\\
=\lim_{h\rightarrow0}\; \frac{-1}{5(5+h)}}\\\\
=\frac{-1}{5(5+0)}}\\\\
=\frac{-1}{25}}\\\\$$

$$The gradient of $ y=\frac{1}{x} $ at $ x=5 $ is $ \frac{-1}{25}$$

Your LaTex is beautiful but the answer is incorrect.   

3x-4y+2+y+8x

think of the x as a xylophone  and the y as a yak

You cannot add xylophones and yaks it just doesn't work!

Lets change the question a little so it makes mores sense.

3x+4y+y+8x

Now you have all these things can you tell me what you have more simply please?

3x-4y+2+y+8x

1/tan(5*pi)

If you sub x=5 back into the formula you will find it does not work.

You have made a mistake somewhere.