Equation of given lines:
→r=^i+2^j+3^k+t(2^i+3^j+4^k)
and →r=2^i+4^j+5^k+s(3^i+4^j+5^k)
∴→a1=^i+2^j+3^k,→b1=2^i+3^j+4^k
and →a2=2^i+4^j+5^k,→b2=3^i+4^j+5^k
∴→a2−→a1=(2^i+4^j+5^k)−(^i+2^j+3^k)
⇒→a2−→a1=^i+2^j+2^k
→b1×→b2=∣∣
∣
∣∣^i^j^k234345∣∣
∣
∣∣
=^i(15−16)−^j(10−12)+^k(8−9)
=^i+2^j−^k
∴|→b1×→b2|=|−^i+2^j−^k|
=√(−1)2+22+(−1)2
=√1+4+1=√6
∴ shortest distance
=(→a2−→a1)(→b1×→b2)|→b1×→b2|
=(^i+2^j+2^k).(−^i+2^j−^k)√6
=−1+4−2√6=1√6.