expansion of (4-5x)^1/2

I know that the genral formular for binomial expansion with rational powers is: (1+x)^n= 1+nx+n(n-1)/2! and so on.
However I dont under stand how the first and second terms of the expansion are 2 and 5/4x. Surely they should be 4 and 5/2x as n in this case is 1/2 and x is 5x. What am i doing wrong here?

Can you show the working and I can highlight the error ? I’m assuming you may have taken the 4 out of the brackets but not taken the power with it….?

So from your working I can see you’ve not manipulated the bracket correctly at the start.
(4-5x)^1/2 , needs to be changed so it’s in the required form to continue if that makes sey

Yes that makes sence, Thankyou. I needed to factor out ther 4 right?

Don't forget the power too ...

ok so i factor out 4^1/2 which is 2. I then do the expansion of (1+5/2x)^1/2. And im assuming that at the end i would multiply all the terms by 4^1/2?