Ta có : \(\left(x-5\right)^4=\left(x-5\right)^6\)
\(\Rightarrow\left(x-5\right)^4-\left(x-5\right)^6=0\)
\(\Leftrightarrow\left(x-5\right)^4\left[1-\left(x-5\right)^2\right]=0\)
\(\Leftrightarrow\orbr{\begin{cases}\left(x-5\right)^4=0\\1-\left(x-5\right)^2=0\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x-5=0\\\left(x-5\right)^2=1\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=5\\\left(x-5\right)=-1;1\end{cases}}\)
\(\Leftrightarrow\orbr{\begin{cases}x=5\\x=4;6\end{cases}}\)
Vậy x = {4;5;6}.
b) Ta có : ax = a50
=> x = 50
d) Ta có : 1 + 2 + 3 + ..... + x = 222111
=> \(\frac{\left[\left(x-1\right):1+1\right]\left(x+1\right)}{2}=222111\)
=> \(\frac{x\left(x+1\right)}{2}=222111\)
=> x(x + 1) = 444222
=> x(x + 1) = 666.667
=> x = 666
Vậy x = 666.
