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urgent coordinate geometry Help please !! watch

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    Hi guys i need urgent help. We have only done 1 lesson on coordinate geometry and i don't understand my task that well. Ive done most of my questions already but there are some i dont know where to begin with. Can someone please guide me through what i should do in the following question?? Any help will be really appreciated and thanks in advance to anyone who does

    question:
    1) the coordinates of two points are A(-1,-3) and B(5,7).

    i) find the equation of the line l perpendicular to AB and passes through the point B.

    ii) the lines l crosses the y axis at point C. Find the area of triangle ABC, simplifying answer.

    So for part 1 do i start by finding the gradient of AB? I got that to be 5/3 so the perpendicular line will have a gradient of -3/5 ?
    Since it passes through B would i do
    y= mx+c
    Where m= -3/5 y= 7 and x= 5
    So c= 10 ??
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    (Original post by Aty100)
    Hi guys i need urgent help. We have only done 1 lesson on coordinate geometry and i don't understand my task that well. Ive done most of my questions already but there are some i dont know where to begin with. Can someone please guide me through what i should do in the following question?? Any help will be really appreciated and thanks in advance to anyone who does

    question:
    1) the coordinates of two points are A(-1,-3) and B(5,7).

    i) find the equation of the line l perpendicular to AB and passes through the point B.

    ii) the lines l crosses the y axis at point C. Find the area of triangle ABC, simplifying answer.

    So for part 1 do i start by finding the gradient of AB? I got that to be 5/3 so the perpendicular line will have a gradient of -3/5 ?
    Since it passes through B would i do
    y= mx+c
    Where m= -3/5 y= 7 and x= 5
    So c= 10 ??
    The first part is correct.
    For the second part, have you found the coordinates of C? Once you've done that, plot the points on a set of axes to see what this triangle looks like and deduce how you might go about finding its area.
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    (Original post by razzor)
    The first part is correct.
    For the second part, have you found the coordinates of C? Once you've done that, plot the points on a set of axes to see what this triangle looks like and deduce how you might go about finding its area.
    Sorry how would i find the coordinates of C ??
    Ive got the equation of the first part as
    Y= -3/5x + 10
    Would the coordinates therefore be 3/5 and -10 ??
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    (Original post by Aty100)
    Sorry how would i find the coordinates of C ??
    Ive got the equation of the first part as
    Y= -3/5x + 10
    Would the coordinates therefore be 3/5 and -10 ??
    It says the graph crosses the y axis at C. When a graph crosses the y axis, x=0. You can use this to find the y coordinate.
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    (Original post by Aty100)
    Sorry how would i find the coordinates of C ??
    Ive got the equation of the first part as
    Y= -3/5x + 10
    Would the coordinates therefore be 3/5 and -10 ??
    We know that this line crosses the y-axis at C, so what x-coordinate does it have?
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    (Original post by razzor)
    We know that this line crosses the y-axis at C, so what x-coordinate does it have?
    Is C (0,10) ??

    Also in the attachment is my attempt at the area,
    I'm not really sure what to do, do we use the formula to find the area of a triangle?
    Attached Images
     
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    (Original post by Aty100)
    Is C (0,10) ??

    Also in the attachment is my attempt at the area,
    I'm not really sure what to do, do we use the formula to find the area of a triangle?
    As to your second question: yes, use 1/2 * base * height
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    (Original post by Zacken)
    As to your second question: yes, use 1/2 * base * height
    But which base x height do I use ??

    So I do

    1/2* 4 * 3 ??
    = 6 ?

    Or

    1/2 * 4 * 13
    =26 ?
    Im lost
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    (Original post by Aty100)
    But which base x height do I use ??

    So I do

    1/2* 4 * 3 ??
    = 6 ?

    Or

    1/2 * 4 * 13
    =26 ?
    Im lost
    Where did the 4 and 13 come from?
    You need to calculate the distance between the coordinates and then apply the area formula.
    Spoiler:
    Show
    Distance between two set of coordinates (x1, x2) and (y1, y2) is given by  \sqrt{(x_{2}-x_{1})^{_{2}}+(y_{2}-y_{1})^{_{2}}}
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    (Original post by razzor)
    Where did the 4 and 13 come from?
    You need to calculate the distance between the coordinates and then apply the area formula.
    Spoiler:
    Show
    Distance between two set of coordinates (x1, x2) and (y1, y2) is given by  \sqrt{(x_{2}-x_{1})^{_{2}}+(y_{2}-y_{1})^{_{2}}}
    Thanks so much,
    I got confused
    So i find the distance between A & C?
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    (Original post by Aty100)
    Thanks so much,
    I got confused
    Spoiler:
    Show
    So i find the distance between A & C?

    Not quite - the distance AC isn't the height of the triangle.
    Have a look where the right-angle is formed (identify which line is l)
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    (Original post by Aty100)
    Is C (0,10) ??

    Also in the attachment is my attempt at the area,
    I'm not really sure what to do, do we use the formula to find the area of a triangle?
    Or you could do this:


    Working out the area of right-angled triangles is probably easier than working out the equation perpendicular line for the height and finding out where it meets the base line and how long it is.
 
 
 
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