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If the points P(8,5), Q(4,8), R(0,5) and S(4,k) are the vertices of a rhombus, taken in order, then the value of k is

Solution

✅ Correct Option: 4

For a rhombus, all four sides are equal in length and the diagonals bisect each other at their midpoint.

Since the vertices are given in order P→Q→R→S, the diagonals are PR and QS.

The diagonals must bisect each other, so:

Midpoint of PR = Midpoint of QS


Finding the midpoint of diagonal PR:

P = (8, 5) and R = (0, 5)

Midpoint of PR =(8+02,5+52)= \left(\dfrac{8+0}{2}, \dfrac{5+5}{2}\right)

=(4,5)= (4, 5)


Finding the midpoint of diagonal QS:

Q = (4, 8) and S = (4, k)

Midpoint of QS =(4+42,8+k2)= \left(\dfrac{4+4}{2}, \dfrac{8+k}{2}\right)

=(4,8+k2)= \left(4, \dfrac{8+k}{2}\right)


Setting the midpoints equal:

(4,5)=(4,8+k2)(4, 5) = \left(4, \dfrac{8+k}{2}\right)

The x-coordinates match. Equating the y-coordinates:

5=8+k25 = \dfrac{8+k}{2}

10=8+k10 = 8 + k

k=2k = 2

Therefore, the value of k=2k = 2.

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