Let R(4, y, z) be any point which divides the join of P(2, –3, 4) and Q(8, 0, 10) in the ratio k : 1 internally. ∴ Coordinates of R are $\left(\frac{8k+2}{k+1},\frac{-3}{k+1},\frac{10k+4}{k+1}\right)$ But x- coordinate of R is 4 ∴ $\frac{8k+2}{k+1}$ = 4 ⇒ 8k + 2 = 4k + 4 ⇒ k = $\frac{1}{2}$ ∴ y = $\frac{-3}{\frac{1}{2}+1}$ = $\frac{-3}{\frac{3}{2}}$ = - 2 z = $\frac{\frac{10\times1}{2}+4}{\frac{1}{2}+1}$ = $\frac{9}{\frac{3}{2}}$ = 6 Thus coordinates of R are (4, – 2, 6).