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  • Perplex
    IB Math AAHL
    /
    Cartesian plane & lines
    /

    Problem Bank

    [Maximum mark: 17]

    The function ​f​ is defined by ​f(x)=log3​(x+1). Triangle ​△OPQ​ is drawn under the graph of ​y=f(x)​ where ​O​ is the origin, ​P​ has a ​y​-coordinate of ​1, and the triangle is right angled at ​Q.

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    1. Find

      1. The coordinates of ​P.

        [2]

        To earn a crown, get your answer ready before you reveal the options!

      2. The ratio ​[OQ][PQ]​​

        [1]

    A second triangle, ​△PRS, is drawn such that ​△PRS​ and ​△OPQ​ are similar, ​S​ lies on the curve of ​y=f(x), and ​R=(r,0), where ​r>2.


    A line ​L​ is drawn passing through the points ​P​ and ​R.

    1. Show that ​L​ has the equation ​y=2−rx−r​.

      [3]
    2. Show that the ​x​-coordinate of ​S​ is ​r+2.

      [7]
    3. By considering the slope of ​RS, show that ​2log3​(r+3)​=r−2.

      [2]
    4. Hence find the value of ​r.

      [2]

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