Solutions to this question by accurate drawing will not be accepted. The diagram shows an isosceles triangle PQR in which . The vertices of the triangle are at the points P(k, 4), Q(5, 3) and R(9, 10).

- (i)
Find the value of k.
- (ii)
A line is drawn from Q to cut the y-axis at S such that .
Find the equation of QS and the coordinates of S.
- (iii)
Find the ratio of the area of triangle PQR to the area of quadrilateral PQRS.
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Worked solution
10(i)
1. Calculate the square of the length of QR
2. Express the square of the length of PQ in terms of k and equate to $QR^2$
Since , .
3. Solve the quadratic equation for k
4. Determine the correct value of k based on the diagram
From the diagram, point P is to the left of the y-axis, so its x-coordinate must be negative ().
Therefore, .
10(ii)
1. Find the coordinates of P from part (i) using the given $PQ = QR$.
Using the distance formula for :
From the diagram, P is to the left of the y-axis, so . Thus, and is .
2. Set up an equation for the coordinates of S using $PS = SR$.
Since S lies on the y-axis, let its coordinates be .
Given , we have :
3. Solve for y to find the coordinates of S.
The coordinates of S are .
4. Find the equation of the line QS.
Using and :
Gradient of QS,
Since S is the y-intercept, the equation of QS is:
Coordinates of S:
Equation of QS:
10(iii)
1. Find the coordinates of P and S from earlier parts
From part (i), is .
From part (ii), is .
The coordinates of the vertices are , , and .
2. Calculate the area of triangle PQR
Using the shoelace formula for with vertices , , :
3. Calculate the area of quadrilateral PQRS
Using the shoelace formula for quadrilateral with vertices , , , :
4. Find the ratio of the areas
Dividing by 15:
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