Condition for a Conic to Be a Pair of Straight Lines
The shortest ...
Question
The shortest distance between the skew lines →r=→r1+t→a1 and →r=→r2+n−→a2,where →r1=9j+2k,→a1=3i−j+k,→r2=−6i−5j+10k,→a2=−3i+2j+4k is 3√a. Then the value of a is:
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Solution
Given →r1=9j+2k,→a1=3i−j+k,→r2=−6i−5j+10k,→a2=−3i+2j+4k, we have: →r2−→r1=−6i−14j+8k
and →a1×→a2=∣∣
∣∣ijk3−11−324∣∣
∣∣=−6i−15j+3k,
So, d=(→r2−→r1).(→a1×→a2)|→a1×→a2|⇒d=(−6)(−6)+(−14)(−15)+(8)(3)√36+225+9⇒d=270√270=√270=3√30⇒a=30