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Question

In parallelogram PQRS, P(-3,2), Q(2,7) and S(1,9) are three vertices. Then the length of diagonal PR is


A
12 units
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B
9 units
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C
15 units
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D
25 units
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Solution

The correct option is C 15 units

Draw PE, SF parallel to x-axis.

Draw QE, RF parallel to y-axis.

Now, in right triangles PEQ and SFR,

PQ = SR

QPE = RSF

PQE = SRF

Therefore, PE = SF and QE = RF .....[by RHS congruency]

Hence, PE = SF = 2 - (-3) = 5 and QE = RF = 7 - 2 = 5

Now, x-coordinate of R = 1 + SF
= 1 + 5
= 6

y-coordinate of R = 9 + RF
= 9 + 5
= 14

Therefore coordinates of R(6,14).

The distance between two points (x1,y1) and (x2,y2) is (x2x1)2+(y2y1)2

PR = (6(3)2+(142)2
= 92+122
= 225
= 15 units


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