A square ABCD of diagonal 2a is folded along the diagonal 2a so that the planes DAC and BAC are at right angle. The shortest distance between DC and AB is
[Kurukshetra CEE 1998]
When folded co - ordinates will be
D(0,0,a); C(a,0,0);
A(-a,0,0); B(0,-a,0)
Equation DC is, xa=y0=z−a−a
Equation AB is, x+aa=y−a=z0
∴ Shortest distance =2a√3, (By formula).