Let the given points be A(1, –1, 2), B(3, 4, –2), C(0, 3, 2) and D(3, 5, 6).The direction ratios of AB are < 3 – 1, 4 + 1, –2 –2 > or <2, 5, – 4> and the direction ratios of CD are < 3 – 0, 5 – 3, 6 – 2 > or <3, 2, 4 > Two lines with direction ratios $a_1, b_1, c_1$ and $a_2, b_2, c_2$ are perpendicular if $a_1a_2 + b_1b_2 + c_1c_2 = 0$⇒ 2 × 3 + 5 × 2 + (–4) × 4 = 6 + 10 – 16 = 0∴ AB and CD are perpendicular.