The orthocentre of the triangle formed by the points (2, –1, 1), (1, –3, –5), (3, –4, –4) is

For the right angled triangle, the ortho center is vertex at right angle

The lengths of the sides of the triangle are as below 

Vertices are $A(2, –1, 1), B(1, –3, –5), C(3, –4, –4)$

$$\begin{gathered} a=BC=\sqrt{4+1+1}=\sqrt{6} \\ b=CA=\sqrt{1+9+25}=\sqrt{35} \\ c=AB=\sqrt{1+4+36}=\sqrt{41} \end{gathered}$$

Observing the above lengths, the sum of the squares of two sides is equal to the square of the third side

Hence, the triangle is right angled triangle. 

Hence, the orthocenter is vertex ar right angle

Therefore, the orthocentre is . $C(3, –4, –4)$