Tetrahedron Problem | AIME I, 1992 | Question 6

Try this beautiful problem from the American Invitational Mathematics Examination I, AIME I, 1992 based on Tetrahedron.

Tetrahedron Problem - AIME I, 1992


Faces ABC and BCD of tetrahedron ABCD meet at an angle of 30,The area of face ABC=120, the area of face BCD is 80, BC=10. Find volume of tetrahedron.

  • is 107
  • is 320
  • is 840
  • cannot be determined from the given information

Key Concepts


Area

Volume

Tetrahedron

Check the Answer


Answer: is 320.

AIME I, 1992, Question 6

Coordinate Geometry by Loney

Try with Hints


Area BCD=80=\(\frac{1}{2} \times {10} \times {16}\),

where the perpendicular from D to BC has length 16.

Tetrahedron Problem

The perpendicular from D to ABC is 16sin30=8

[ since sin30=\(\frac{perpendicular}{hypotenuse}\) then height = perpendicular=hypotenuse \(\times\) sin30 ]

or, Volume=\(\frac{1}{3} \times 8 \times 120\)=320.

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Triple Integral | IIT JAM 2016 | Question 15

Question 15 - Triple Integral (IIT JAM 2016)


If the triple integral over the region bounded by the planes $2x+y+z=4$ $x=0$ $y=0$ $z=0$ is given by $\int\limits_0^2\int\limits_0^{\lambda(x)}\int\limits_0^{\mu(x,y)}\mathrm d z\mathrm d y\mathrm d x$ then the function $\lambda(x)-\mu(x,y)$ is

  • $x+y$
  • $x-y$
  • $x$
  • $y$

Key Concepts


Real Analysis

Integral Calculus

Triple Integral

Check the Answer


Answer: $\textbf{(B)} \quad y$

IIT JAM 2016, Question No. 15

Differential and Integral Calculus: R Courant

Try with Hints


Here we are given with triple integral over the region bounded by the planes $2x+y+z=4, x=0, y=0$ and $z=0$

Now we our aim here is to find $\lambda (x) $ and $\mu(x,y)$. Now we will approach this problem by find the volume of $(x,y,z)$ based on $2x+y+z=4$ can you do this ??? (With the given information x=0, y=0, z=0)

$2x+y+z=4$

$\Rightarrow z=4-2x-y$

$\Rightarrow 2x+y=4$ [as $z=0$]

$\Rightarrow y=4-2x$

Again,

$2x+y+z=4$

Now as $y=z=0$ we have $2x=4$

Therefore $x=2$

Now can you use this to move forward with this problem ?

So our triple integral become,

$\int_0^2\int_0^{(4-2x)}\int_0^{(4-2x-y)}\mathrm d z\mathrm d y\mathrm dx$

On compairing $\lambda(x)=4-2x$ and $\mu(x,y)=4-2x-y$

Therefore $\lambda(x)-\mu(x,y)=4-2x-4+2x+y=y$ (ANS)

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