Skip to main contentSkip to solution

The sum of length, breadth and height of a cuboid is 22 cm and length of its body diagonal is 14 cm. if S is the sum of cubes of dimensions of the cuboid and V is the volume, the (S−3V) will be equal to

Solution

✅ Correct Option: 4

l+b+h=22l+b+h=22

Using the formula for the body diagonal of a cuboid, l2+b2+h2\sqrt{l^2+b^2+h^2}:

l2+b2+h2=14\sqrt{l^2+b^2+h^2}=14

⇒l2+b2+h2=196\Rightarrow l^2+b^2+h^2=196


Using the identity (l+b+h)2=l2+b2+h2+2(lb+bh+hl)(l+b+h)^2=l^2+b^2+h^2+2(lb+bh+hl):

484=196+2(lb+bh+hl)484=196+2(lb+bh+hl)

⇒2(lb+bh+hl)=288\Rightarrow 2(lb+bh+hl)=288

⇒lb+bh+hl=144\Rightarrow lb+bh+hl=144


Here S=l3+b3+h3S=l^3+b^3+h^3 and V=lbhV=lbh, so S−3VS-3V is exactly the left side of the identity

l3+b3+h3−3lbh=(l+b+h)(l2+b2+h2−lb−bh−hl)l^3+b^3+h^3-3lbh=(l+b+h)\left(l^2+b^2+h^2-lb-bh-hl\right)

S−3V=22(196−144)S-3V=22(196-144)

=22×52=22\times52

=1144=1144

S−3V=1144 cm3S-3V=1144\text{ cm}^3

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question