i looking over my maths books and lecture notes for an exam i have next week but i am cofused about an element of newton raphson as there seems to be 2 paths to finding some answers

f(x) = 8x^4=0.45x^3-4.544x-0.1136, x=0.8

when looking at this i was given the equation "x - f(x)/f'(x) = xf'(x)-f(x)/f'(x)"

i have used this equation for this example but when i try to use it for an example such as :

f(x)=4x^3-2x^2-200x-50, x=7 i have to use the standard equation
(xn+1 = xn-(f(x)/f'(x)) or i get a completely wrong answer

the questions are worded exactly the same but if i try to use the same method for both i end up with a wrong answer for the latter, i'm really confused please help (ps answers are 0.8182 and 6.951)