wiz-icon
MyQuestionIcon
MyQuestionIcon
8
You visited us 8 times! Enjoying our articles? Unlock Full Access!
Question

If volume of regular tetrahedron of edge length k is V and shortest distance between any pair of opposite edges of same regular tetrahedron is d, then the value of d3V is

Open in App
Solution

Length of edge of regular tetrahedron =k
Consider a tetrahedron ABCD
and let A(0,0,0), B(k,0,0), C(k2,3k2,0)
Projection of point D on plane containing points A,B and C is the centroid of equilateral triangle ABC
Projection of D is (k2,3k6,0)
Let coordinates of D be (k2,3k6,h)

|AD|=k
k24+k212+h2=k2
h2=k2k23=2k23
h=23k
D is (k2,3k6,2k3)

Since, distance between any two skew lines of tetrahedron ABCD=d,
ACCD×ABCD×AB=d
d=(k2^i+3k2^j)(23k6^j+2k3^k)×k^i∣ ∣(236^j+2k3^k)×k^i∣ ∣
d=(k2^i+3k2^j)(23k26^k+2k23^j)k2 (13)2+(23)2
=3k2.2k23k2
d=12k

Area of equilateral ΔABC=34k2
Volume of tetrahedron, V=13×(ar(ΔABC))×h
=13×34k2×23k=2k312

d3V=(k2)3(2k312)
=k322.122k2=124=3

Alternate Solution :

We first draw a cube of side length d and draw a tetrahedron in it.
By Pythagoras theorem,
d2+d2=DC2=k2
d=k2

Volume of regular tetrahedron with edge length k is V=k362
d3V=3

flag
Suggest Corrections
thumbs-up
0
Join BYJU'S Learning Program
similar_icon
Related Videos
thumbnail
lock
Tetrahedron
MATHEMATICS
Watch in App
Join BYJU'S Learning Program
CrossIcon