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Straight Lines Test -6

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Straight Lines Test -6
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  • Question 1
    1 / -0

    The image of the point ( -1 , 2 ) in the origin is

    Solution

    when a point M which is in the 2nd quadrant is reflected in the origin, its image is formed in the 4th quadrant whose coordinates are (x,-y)

    Hence the image of the point (1,-2) is (1,-2)

  • Question 2
    1 / -0

    The orthogonal projection of the point ( 2 , - 3 ) on the line x + y = 0 is

    Solution

    Equation of the line which perpendicular to the given line is x - y + k = 0

    Since this line passes through (2,-3)

    2-(-3) + k = 0

    This implies k= -5

    Hence the equation og the line is x - y =5

    On solving the lines x+y=0 and x-y=5, we get the point of intersection as x = 5/2 and y = -5/2

    Hence (5/2,-5/2) is the coordinates of orthogonal projection.

  • Question 3
    1 / -0

    Three points A , B and C are collinear if the area of triangle ABC is

    Solution

    Only non collinear points can form a triangle. Hence if the three points are collinear  a triangle cannot be formed, hence  the area of the triangle is zero

  • Question 4
    1 / -0

    The number of points on X axis which are at a distance of c units ( c < 3 ) from ( 2 , 3 ) is

    Solution

    Let (x,0) be the point.

    Then (by distance formula,

    (x-2)2 +32 = c2

    x2 -4x +4 + 9 - c2 = 0

    x2 - 4x +13 - c2 = 0

    x will be real if the b2 - 4ac  ≥≥0

    i.e; 16 - 4(13 - c2) ≥≥ 0

    i.e; c2 - 9 ≥≥ 0

    i.e; |c| ≥≥ 3

    Hence there is no point.

  • Question 5
    1 / -0

    The equations of the lines through ( 1 , 1 ) and making angles of 450 with the line x + y = 0

    Solution

    If the lines make equal angles of 450 with the given line, x+y =0.

    Then these lines must be perpendicular with each other.

    This is possible only when the two lines are parallel to X axis and Y axis.

    That is the equations should be x = a constant and y  = a constant.

    Since it passes through (1,1)

    The equations should be x = 1 or x-1=0 and y=1 or y-1 =0

     

  • Question 6
    1 / -0

    The number of lines that are parallel to 2x + 6y – 7 = 0 and have an intercept 10 units between the coordinate axis is :

    Solution

    Thslope of the given line 2x+6y = 7 is -1/3

    Hence the line which is parallel to the above line is 

    y = (-1/3)x+c

    That is the y intercept is (0,c) and the x intercept is (3c,0)

    Using the distance formula

    d2 = (0-3c)2 + (3c-0)2

    = 10c2

    since the distance is 10 is given,

    100 = 10c2

    therefore c = ±±10

    Since two values are possible, two lines can be drawn.

  • Question 7
    1 / -0

    The line ( p + 2q ) x + ( p – 3q ) y = p - q for different values of p and q passes through the fixed point

    Solution

    Expanding the given equation

    px+2qx+py-3qy = p-q

    px+py+2qx-3qy = p-q

    p(x+y) -q(-2x+3y) = p-q

    Equating the coeffiecients of like terms

    x+y=1 and -2x+3y=1

    On solving both the equations we get,

    x = 2/5 and y = 3/5

    Hence the line passes through the fixed point (2/5.3/5)

  • Question 8
    1 / -0
    How far is the line 3x - 4y + 15 = 0 from the origin?
    Solution
    Distance of $$O(0,0)$$ from the line $$3x-14y+15=0$$ is

    $$=>r=\dfrac{|3(0)-4(0)+15|}{\sqrt {3^3+4^2}}$$

    $$=>r=\dfrac{15}{\sqrt {25}}$$

    $$=>r=\dfrac{15}{5}$$

    $$=>r=3$$
  • Question 9
    1 / -0
    The point $$(0,\,5)$$ lies on the line $$x+y=5$$ or not
    Solution
    Given the line $$x+y=5$$
    when$$ x=0 ,y =5 \Rightarrow(0,5)$$
    $$\therefore$$ The point (0,5) lies on the line$$ x+y=5$$
  • Question 10
    1 / -0
    Which of the following is perpendicular to the line x/3 + y/4 = 1?
    Solution
    Line is
    $$\frac{x}{3}+\frac{y}{4}=1$$
    $$=>4x+3y=12$$
    $$=>3y=-4x+12$$
    $$=>y=\frac{-4}{3}+4$$
    Here $$m=\frac{-4}{3}$$
    $$\therefore$$ Slope of line perpendicular to given line is $$\frac{3}{4}$$
    Option A
    $$x-4y-8=0$$
    $$=>y=\frac{-x}{4}-\frac{8}{4}$$ (not perpendicular)
    Option B
    $$4x-3y-6=0$$
    $$=>y=\frac{4x}{3}-\frac{6}{3}$$ (not perpendicular)
    Option C
    $$3x-4y-11=0$$
    $$=>y=\frac{3}{4}x-\frac{5}{4}$$ (perpendicular)
    Option D
    $$4x+3y-11=0$$
    $$=>y=\frac{-4}{3}x+\frac{11}{4}$$ (not perpendicular)

  • Question 11
    1 / -0
    Find the distance from the point (5, -3) to the line 7x - 4y - 28 = 0
    Solution
    Distance of point $$(5,-3)$$ from the line $$7x-4y-28=0$$ is

    $$=>r=\dfrac{|7(5)-4(-3)-28|}{\sqrt {7^2+4^2}}$$

    $$=>r=\dfrac{|35+12-281|}{\sqrt {49+16}}$$

    $$=>r=\dfrac{19}{\sqrt 65}$$

    $$=>r=\dfrac{19}{8.06}$$

    $$=>r=2.36$$
  • Question 12
    1 / -0
    Determine the distance from (5, 10) to the line x - y = 0
    Solution
    Distance of point $$(5,10)$$ from the line $$x-y=0$$ is

    $$r=\dfrac{|5-10|}{\sqrt {1^2+1^2}}$$

    $$=>r=\dfrac{|-5|}{\sqrt 2}$$

    $$=>r=\dfrac{5}{\sqrt 2}$$

    $$=>r=3.54$$
  • Question 13
    1 / -0
    A line is of length $$10$$ and one end is $$(2,-3)$$. If the abscissa of the other end is $$10$$, then find its ordinate.
    Solution
    Coordinates are $$(10,y)$$
    $$\Rightarrow \sqrt{(10-2)^{2}+(y+3)^{2}}=10$$
    $$\Rightarrow (y+3)^{2}=6^{2}\Rightarrow y+3=\pm 6$$
    $$y=3$$ or $$-9$$
  • Question 14
    1 / -0
    The distance between $$M(-1,5)$$ and $$N(x,5)$$ is $$8$$ units. The value of $$x$$ is:
    Solution
    $$\sqrt{[x-(-1)]^{2}+(5-5)^{2}}=8$$
    $$\Rightarrow (x+1)^{2}=8^{2}\Rightarrow x+1=\pm 8$$
    $$\therefore x=-9,7$$
  • Question 15
    1 / -0
    In the diagram $$MN$$, is a straight line.
    The distance between $$M$$ and $$N$$ is:

    Solution
    $$\sqrt{(3+3)^{2}+(2+6)^{2}}$$
    $$\Rightarrow \sqrt{36+64}\Rightarrow 10$$
  • Question 16
    1 / -0
    $$P$$ is the point $$(-5,3)$$ and $$Q$$ is the point $$(-5,m)$$. If the length of the straight line $$PQ$$ is $$8$$ units, then the possible value of $$m$$ is:
    Solution
    $$\sqrt{(-5-(-5))^{2}+(m-3)^{2}}=8$$
    $$\Rightarrow (m-3)^{2}=8^{2}$$
    $$\Rightarrow m-3=\pm 8$$
    $$\Rightarrow m=-5+11$$
  • Question 17
    1 / -0
    In the diagram, $$PQ=PR$$
    Find the value of $$h$$.

    Solution
    As PQ=PR
    $$\sqrt{(h+2)^{2}+(5-1)^{2}}=\sqrt{(h-4)^{2}+(5-1)^{2}}$$
    squaring both sides
    $$(h+2)^{2}+4^{2}=(h-4)^{2}+4^{2}$$
    $$h^{2}+4+4h=h^{2}+16-8h$$
    $$\Rightarrow 12h=12\Rightarrow h=1$$
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