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In the given figure, △PQR is equilateral. If the coordinates of the points Q and R are (0, 2) and (0, -2) respectively, find the coordinates of the point P.

In the given figure, △PQR is equilateral. If the coordinates of the points Q and R are (0, 2) and (0, -2) respectively, find the coordinates of the point P. Coordinate Geometry, ML Aggarwal Understanding Mathematics Solutions ICSE Class 9.

Coordinate Geometry

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Answer

Given, PQR is an equilateral triangle in which Q(0, 2) and R(0, -2) and O = (0, 0).

Let (x, 0) be the coordinates of P. [As, P lies on x axis, so y-coordinate is zero.]

By distance formula,

QR=(x2x1)2+(y2y1)2=(00)2+(22)2=0+(4)2=16=4 units.OQ=(x2x1)2+(y2y1)2=(00)2+(20)2=0+(2)2=4=2 units.\Rightarrow QR = \sqrt{(x2 - x1)^2 + (y2 - y1)^2} \\[1em] = \sqrt{(0 - 0)^2 + (-2 - 2)^2} \\[1em] = \sqrt{0 + (-4)^2} \\[1em] = \sqrt{16} \\[1em] = 4 \text{ units}. \\[1em] \Rightarrow OQ = \sqrt{(x2 - x1)^2 + (y2 - y1)^2} \\[1em] = \sqrt{(0 - 0)^2 + (2 - 0)^2} \\[1em] = \sqrt{0 + (2)^2} \\[1em] = \sqrt{4} \\[1em] = 2 \text{ units}.

PQ = PR = QR = 4.

OQ = 2

In right angle triangle POQ,

⇒ PQ2 = OP2 + OQ2 [By pythagoras theorem]

⇒ 42 = OP2 + 22

⇒ 16 = OP2 + 4

⇒ OP2 = 16 - 4

⇒ OP2 = 12

⇒ OP = 12=23\sqrt{12} = 2\sqrt{3}.

Since, P lies on x-axis and OP = 232\sqrt{3}.

Hence, the coordinates of P are (232\sqrt{3}, 0).

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