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Coordinate Geometry Test - 23

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Coordinate Geometry Test - 23
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  • Question 1
    1 / -0
    If $$(a, b)$$ is the mid-point of the line segment joining the points $$A (10, 6)$$ and $$B (k, -4)$$ and $$a+  2b = 18,$$ find the value of $$k.$$
    Solution
    Let the point $$P(x,y)=(a,b)$$ the line segment $$AB$$ joining the points $$A\left( { x }_{ 1 },{ y }_{ 1 } \right) =\left( 10,6 \right)    \&    B\left( { x }_{ 2 },{ y }_{ 2 } \right) =\left( k,-4 \right)$$ in   the   ratio   $$m:n=1:1$$

    Then,   by   the   section   formula,  
    $$x=\dfrac { n{ x }_{ 2 }+m{ x }_{ 1 } }{ m+n } =\dfrac { { x }_{ 2 }+{ x }_{ 1 } }{ 2 }$$

    $$\Rightarrow a=\dfrac { 10+k }{ 2 } \Rightarrow k=2a-10$$  ...(i)

    $$y=\dfrac { n{ y }_{ 1 }+m{ y }_{ 2 } }{ m+n } \Rightarrow b=\dfrac { 6-4 }{ 2 } =1$$ 

    But   given   that $$a+2b=18\Rightarrow a=18-2b=18-2\times 1=16$$

    Substituting   $$a=16$$   in   (i)   we   get   $$k=2\times 16-10=22$$

    Hence, option C.
  • Question 2
    1 / -0
    The point which divides the line joining the points $$A(1, 2)$$ and $$B(-1, 1)$$ internally in the ratio $$1:2$$ is
    Solution

    Let the given point $$C$$ divide  $$A(1,2)$$ and $$B(-1, 1)$$ internally in the ratio $$1:2$$. 

    Therefore, we have $$m=1$$ and $$n=2$$.

    By section formula for internal division, the point $$C(x,y)$$ is 

    $$x=\dfrac{(mx_{2}+nx_{1}) } {(m+n)}$$ and $$y=\dfrac{(my_{2}+ny_{1}) } {(m+n)}$$

    $$x=\dfrac{(-1 \times 1+2 \times 1) } {(1+2)}$$ and $$y=\dfrac{(1 \times 1+2\times 2) } {(1+2)}$$

    $$ \therefore x=\dfrac{1}{3}$$ and $$y=\dfrac{5}{3}$$

  • Question 3
    1 / -0
    If $$P\left(\dfrac{a}{2},4\right)$$ is the mid-point of the line-segment joining the points A(-6,5) and B(-2,3), then the value of a is
    Solution
    Given P is the mid point of AB,where $$A(-6,5)$$ and $$B(-2,3)$$
    $$\therefore$$  $$\dfrac { a }{ 2 } =\dfrac { -6+(-2) }{ 2 } $$
    $$\therefore  a=-8$$

  • Question 4
    1 / -0
    The area of triangle ABC (in sq. units) is :

    Solution
    The area of a triangle is given as:
    Area $$=\dfrac { 1 }{ 2 } \left[ { x }_{ 1 }({ y }_{ 2 }-{ y }_{ 3 })+{ x }_{ 2 }({ y }_{ 3 }-{ y }_{ 1 })+{ x }_{ 3 }({ y }_{ 1 }-{ y }_{ 2 }) \right] $$
    the given points are $$ A(1,3),~B(-1,0) $$and $$C(4,0)$$
    by Substituting ,
    $$\text{Area} =\dfrac { 1 }{ 2 } \left[ 1(0-0)+(-1)(0-3)+4(3-0) \right] \\ =\dfrac { 1 }{ 2 } \left[ 3+12 \right] =\dfrac { 15 }{ 2 } =7.5$$ 
    $$\therefore$$ Area of the given triangle ABC is $$7.5$$ sq. units
  • Question 5
    1 / -0
    Find the mid point of (3,8) and (9,4).
    Solution
    Midpoint formula is given by $$\left(\dfrac{x_1+x_2}{2},\dfrac{y_1+y_2}{2} \right)$$
    So midpoint of $$(3,8)$$ and $$(9,4)$$ is $$=\left(\dfrac{3+9}{2},\dfrac{8+4}{2} \right)=(6,6)$$
  • Question 6
    1 / -0
    C is the mid-point of PQ, if P is $$(4, x)$$, C is $$(y, -1)$$ and Q is $$(-2, 4)$$, then x and y respectively are-
    Solution
    Given C is the mid point of PQ
    i.e.P(4,x) and Q(-2,4)
    For finding y, equate the (x-coordinates)
    y = $$\dfrac { 4+(-2) }{ 2 } =1$$
    For finding x,equate the y - coordinates
    $$\dfrac { x+4 }{ 2 } =-1\\ \therefore x=-6$$
    $$\therefore x = -6$$
    $$\therefore$$ x and y are $$-6$$ and $$1$$ respectively.

  • Question 7
    1 / -0
    Area of the triangle formed by the points P(-1.5, 3), Q(6, -2) and R(-3, 4) is 0.
    Solution
    We know that the area of the triangle whose vertices are $$\displaystyle (x_{1},y_{1}),(x_{2},y_{2}),$$ and $$(x_{3},y_{3})$$ is $$\cfrac{1}{2}\left | x_{1}(y_{2}-y_{3})+x_{2}(y_{3}-y_{1}) +x_{3}(y_{1}-y_{2})\right |$$
    Given $$P(-1.5, 3), Q(6, -2)$$ and $$R(-3, 4)$$
    Therefore, area is given by
    $$= \frac{1}{2}\times[(-1.5)(-2-4) + 6(4-3)+(-3)(3+2)]$$
    $$= \frac{1}{2}\times(9 +6-15)$$
     $$= 0$$
  • Question 8
    1 / -0
    Coordinates of the points which divides the join of $$(-1, 7)$$ and $$(4, -3)$$ in the ratio $$2:3$$ are $$(1, 3).$$
    Solution
    We know that, the coordinates of the point dividing the line segment joining the points $$({x_1,y_1})$$ and $$({x_2,y_2})$$ in the ratio m:n is given by $$(\frac {m_1x_2+m_2x_1}{m_1+m_21}, \frac {m_1y_2+m_2y_1}{m_1+m_2})$$

    Given $${(x_1,y_1)}= (-1,7)$$; $${(x_2,y_2)} = (4,-3)$$ 
    $${(m_1,m_2)}= 2:3$$
    Coordinates of point of intersection of line segment is
    $$(\frac {(2)(4)+ (3)(-1)}{2+3}, \frac {(2)(-3)+(3)(7)}{2+3})$$
    $$= (5/5,15/5)$$
    $$= (1,3)$$
  • Question 9
    1 / -0
    If A(2, 4), B(6, 10), then find the midpoint of AB.
    Solution
    Given points are $$A(2, 4)$$ and $$B(6,10)$$.

    To find out,
    The coordinates of the midpoint of $$AB$$.

    Let the coordinates of the midpoint be $$(h,k)$$.

    We know that the coordinates of the midpoint of the line segment joining $$(x_1,y_1) \ and\ (x_2,y_2)$$ are: 

    $$P(x,y)=\left(\dfrac{x_1+x_2}{2}, \dfrac{y_1+y_2}{2}\right)$$

    Here, $$x_1=2,\ y_1=4,\ x_2=6,\ y_2=10,\ x=h,\ y=k$$

    Hence, $$(h,k)=\left(\dfrac{2+6}{2}, \dfrac{4+10}{2}\right)$$

    $$\Rightarrow (h,k)=\left(\dfrac{8}{2}, \dfrac{14}{2}\right)$$

    $$\Rightarrow (h,k)=\left(4, 7\right)$$

    Hence, the coordinates of the midpoint of $$AB$$ are $$(4,7)$$.
  • Question 10
    1 / -0
    Find the mid point of $$(4,6)$$ and $$(2,-6)$$.

    Solution
    We know that end points of a line segment is $$(a,b)$$ and $$(c,d)$$, then the midpoint of the line segment has the coordinates:
    $$\dfrac{a+c}{2},\dfrac{b+d}{2}$$
    Then mid point of line segment $$(4,6)$$ and $$(2,-6)$$ is 
    $$\dfrac{4+2}{2},\dfrac{6-6}{2}$$
    $$\Rightarrow \dfrac{6}{2},\dfrac{0}{2}$$
    $$\Rightarrow (3,0)$$
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