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Previous Year Question (PYQs)
3
A ball is thrown upwards from the plane surface of the ground.
Suppose the plane surface from which the ball is thrown consists of the points
$A(1,0,2),\; B(3,-1,1)$ and $C(1,2,1)$ on it.
The highest point of the ball takes is $D(2,3,1)$ as shown in the figure.
Using this information answer the question.
The coordinates of the foot of the perpendicular drawn from the maximum height of the ball to the ground are:
Solution
Plane through points $A,B,C$
$3x+2y+4z=11$
Normal vector of plane
$\vec{n}=(3,2,4)$
Point
$D(2,3,1)$
Foot of perpendicular formula
$\left(x_1-\frac{a(ax_1+by_1+cz_1+d)}{a^2+b^2+c^2},\;
y_1-\frac{b(ax_1+by_1+cz_1+d)}{a^2+b^2+c^2},\;
z_1-\frac{c(ax_1+by_1+cz_1+d)}{a^2+b^2+c^2}\right)$
Plane
$3x+2y+4z-11=0$
Substitute point $D$
$3(2)+2(3)+4(1)-11$
$=6+6+4-11$
$=5$
Denominator
$3^2+2^2+4^2$
$=9+4+16$
$=29$
Coordinates of foot
$x=2-\frac{3(5)}{29}=\frac{43}{29}$
$y=3-\frac{2(5)}{29}=\frac{77}{29}$
$z=1-\frac{4(5)}{29}=\frac{9}{29}$
Foot of perpendicular
$\left(\frac{43}{29},\frac{77}{29},\frac{9}{29}\right)$
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