Exercise 20.4
Page no 20.37
Question 1
Find the area of the triangle whose vertices are :
(i) $(3,-4),(7,5),(-1,10)$
(ii) $\left(a t_{1}^{2}, 2 a t_{1}\right),\left(a t_{2}^{2}, 2 a t_{2}\right),\left(a t_{3}^{2}, 2 a t_{3}\right)$
(iii) $(a \cos \alpha, b \sin \alpha),(a \cos \beta, b \sin \beta),(a \cos \gamma, b \sin \gamma)$
Question 2
Find the area of the quadrilateral whose vertices are :
(i) $(1,1),(7,-3),(12,2)$ and $(7,21)$;
(ii) $(-4,5),(0,7),(5,-5)$ and $(-4,-2)$
Question 3
Find the area of the pentagon whose vertices are $(4,3),(-5,6),(0,-7)$, $(3,-6),(-7,-2)$.
Question 4
Find the area of the hexagon whose consecutive vertices are $(5,0)$, $(4,2),(1,3),(-2,2),(-3,-1)$ and $(0,-4)$
Question 5
If $A, B, C$ are the points $(-1,5) ;(3,1) ;(5,7)$ respectively and $D, E, F$ are the middle points of $B C, C A$ and $A B$ respectively, prove that
$\triangle A B C=4 \triangle D E F \text {. }$
Question 6
Three vertices of a triangle are $A(1,2), B(-3,6)$ and $C(5,4)$. If $D, E$ and $F$ are the mid-points of the sides opposite to the vertices $A, B$ and $C$, respectively, show that the area of triangle $A B C$ is four times the area of triangle $D E F$.
Question 7
Find the area of a triangle $A B C$ if the coordinates of the middle points of the sides of the triangle are $(-1,-2),(6,1)$ and $(3,5)$.
Question 8
The vertices of a $\triangle A B C$ are $A(3,0), B(0,6)$ and $C(6,9)$. A straight line $D E$ divides $A B$ and $A C$ in the ratio $1: 2$ at $D$ and $E$ respectively, prove that
$\frac{\triangle A B C}{\triangle A D E}=9$
Page no 20.38
Question 9
If $(t, t-2),(t+3, t)$ and $(t+2, t+2)$ are the vertices of a triangle, show that it area is independent of t.
Question 10
If $A(x, y), B(1,2)$ and $C(2,1)$ are the vertices of a triangle of area 6 square unit show that $x+y=15$ or $-9$
$\left[\mathrm{HO}_{7} \mathrm{~s},\right.$,
Question 11
Prove that the points $(a, b+c),(b, c+a)$ and $(c, a+b)$ are collinear.
Question 12
If the points $\left(x_{1}, y_{1}\right),\left(x_{2}, y_{2}\right)$ and $\left(x_{3}, y_{3}\right)$ be collinear, show that
$\frac{y_{2}-y_{3}}{x_{2} x_{3}}+\frac{y_{3}-y_{1}}{x_{3} x_{1}}+\frac{y_{1}-y_{2}}{x_{1} x_{2}}=0$
Question 13
If the points $(a, b),\left(a_{1}, b_{1}\right)$ and $\left(a-a_{1}, b-b_{1}\right)$ are collinear, show that $\frac{a}{a_{1}}=\frac{b}{b}$
Question 14
Three points $A\left(x_{1}, y_{1}\right), B\left(x_{2}, y_{2}\right)$ and $C(x, y)$ are collinear. Prove the $\left(x-x_{1}\right)\left(y_{2}-y_{1}\right)=\left(x_{2}-x_{1}\right)\left(y-y_{1}\right)$.
Question 15
Show that the points $(a, 0),(0, b)$ and $(1,1)$ are collinear if $\frac{1}{a}+\frac{1}{b}=1$.
Question 16
Find the values of $x$ if the points $(2 x, 2 x),(3,2 x+1)$ and $(1,0)$ are collinear.
Question 17
Show that the straight line joining the points $A(0,-1)$ and $B(15,2)$ divides ftc line joining the points $C(-1,2)$ and $D(4,-5)$ internally in the ratio $2: 3$.
Question 18
Find the area of the triangle whose vertices are $(a+1)(a+2),(a+2),(a+2)$ $(a+3),(a+3)$ and $(a+3)(a+4),(a+4)$.
Question 19
The point $A$ divides the join of $P(-5,1)$ and $Q(3,5)$ in the ratio $k: 1$ Find the two values of $k$ for which the area of $\triangle A B C$, where $B$ is $(1,5)$ and $C$ is $(7,-2)$ is equal to 2 units in magnitude.
Question 20
The coordinates of $A, B, C, D$ are $(6,3),(-3,5),(4,-2)$ and $(x, 3 x)$ respectively, If $\frac{\triangle D B C}{\triangle A B C}=\frac{1}{2}$, find $x$.
Question 21
If the area of the quadrilateral whose angular points taken in order are $(1,2)$. $(-5,6),(7,-4)$ and $(h,-2)$ be zero, show that $h=3$.
Question 22
Find the area of the triangle whose vertices $A, B, C$ are $(3,4),(-4,3),(8,6)$ respectively and hence find the length of perpendicular from $A$ to $B C$.
Question 23
The coordinates of the centroid of a triangle and those of two of its vertices are respectively $\left(\frac{2}{3}, 2\right),(2,3),(-1,2)$. Find the area of the triangle.
Question 24
The area of a triangle is 3 square units two of its vertices are $A(3,1), B(1,-3)$ and the centroid of the triangle lies on $x$-axis. Find the coordinates of the third vertex $C$.
Question 25
The area of a parallelogram is 12 square units. Two of its vertices are the points $A(-1,3)$ and $B(-2,4)$. Find the other two vertices of the parallelogram, if the point of intersection of diagonals lies on $x$-axis on its positive side.
Question 26
The area of a triangle is $\frac{3}{2}$ square units. Two of its vertices are the point $A(2,-3)$ and $B(3,-2)$, the centroid of the triangle lies on the line $3 x-y-8=0$ Find the third vertex. $C$.
Question 27
Prove that the quadrilateral whose vertices are $A(-2,5), B(4,-1), C(9,1) and $D(3,7)$ is a parallelogram and find its area. If $E$ divides $A C$ in the ratio $2:$ prove that $D, E$ and the middle point $F$ of $B C$ are collinear.
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