=λ The coordinates of any point on the line BC are, (2λ,8λ−11,−3λ+4) Thus, the coordinated of D are, (2λ,8λ−11,−3λ+4) DR's of BC are 2,8,−3 and DR's of AD are 2λ−1,8λ−19,−3λ Also AD is perpendicular to BC, 2(2λ−1)+8(8λ−19)+(−3)(−3λ)=0 4λ−2+64λ−152+9λ=0 77λ=154 λ=2