Maths Olympiad Prep

Library / /202 of 520

Geometry Difficulty 5.4 AIME, harder Find the answer

## Problem Statement

Find the distance from point M0M_{0} to the plane passing through three points M1,M2,M3M_{1}, M_{2}, M_{3}.

M1(2;4;3)M_{1}(2 ;-4 ;-3)

M2(5;6;0)M_{2}(5 ;-6 ; 0)

M3(1;3;3)M_{3}(-1 ; 3 ;-3)

M0(2;10;8)M_{0}(2 ;-10 ; 8)

A number or a short expression. Spacing and $ signs are ignored.

Solution

## Solution

Find the equation of the plane passing through three points M1,M2,M3M_{1}, M_{2}, M_{3}:

x2y(4)z(3)526(4)0(3)123(4)3(3)=0\left|\begin{array}{ccc}x-2 & y-(-4) & z-(-3) \\ 5-2 & -6-(-4) & 0-(-3) \\ -1-2 & 3-(-4) & -3-(-3)\end{array}\right|=0

Perform transformations:

x2y+4z+3323370=0(x2)2370(y+4)3330+(z+3)3237=0 \begin{aligned} & \left|\begin{array}{ccc} x-2 & y+4 & z+3 \\ 3 & -2 & 3 \\ -3 & 7 & 0 \end{array}\right|=0 \\ & (x-2) \cdot\left|\begin{array}{cc} -2 & 3 \\ 7 & 0 \end{array}\right|-(y+4) \cdot\left|\begin{array}{cc} 3 & 3 \\ -3 & 0 \end{array}\right|+(z+3) \cdot\left|\begin{array}{cc} 3 & -2 \\ -3 & 7 \end{array}\right|=0 \end{aligned}

(x2)(21)(y+4)9+(z+3)15=021x+429y36+15z+45=021x9y+15z+51=07x3y+5z+17=0 \begin{aligned} & (x-2) \cdot(-21)-(y+4) \cdot 9+(z+3) \cdot 15=0 \\ & -21 x+42-9 y-36+15 z+45=0 \\ & -21 x-9 y+15 z+51=0 \\ & -7 x-3 y+5 z+17=0 \end{aligned}

The distance dd from a point M0(x0;y0;z0)to the plane Ax+By+Cz+D=0M_{0}\left(x_{0} ; y_{0} ; z_{0}\right)_{\text {to the plane }} A x+B y+C z+D=0:

d=Ax0+By0+Cz0+DA2+B2+C2d=\frac{\left|A x_{0}+B y_{0}+C z_{0}+D\right|}{\sqrt{A^{2}+B^{2}+C^{2}}}

Find:

d=723(10)+58+17(7)2+(3)2+52=14+30+40+1749+9+25=7383 d=\frac{|-7 \cdot 2-3 \cdot(-10)+5 \cdot 8+17|}{\sqrt{(-7)^{2}+(-3)^{2}+5^{2}}}=\frac{|-14+30+40+17|}{\sqrt{49+9+25}}=\frac{73}{\sqrt{83}}

## Problem Kuznetsov Analytic Geometry 8-14

Want a route through all this instead of an archive? The track puts 2,000 problems in a working order, from AMC 10 level to the IMO shortlist.

Source: NuminaMath-1.5, licensed Apache-2.0. Statement and solution reproduced as published; topic and difficulty added by this site.