Shortcut Trick
In a triangle, the coordinates of the centroid are the average of the coordinates of its vertices.
Sum of x-coordinates = 3 × x-coordinate of Centroid.
⇒ x + 5 + 2 = 3 × 4 ⇒ x + 7 = 12 ⇒ x = 5
Sum of y-coordinates = 3 × y-coordinate of Centroid.
⇒ y + (−1) + 6 = 3 × 2 ⇒ y + 5 = 6 ⇒ y = 1
∴ The correct answer is (5, 1).
Alternate Method
P(x, y) Q(5, −1) R(2, 6) G(4, 2)
Given:
Vertices of the triangle: P(x, y), Q(5, −1), and R(2, 6)
Centroid of the triangle: G(4, 2)
Formula Used:
The coordinates of the Centroid G(X, Y) of a triangle with vertices (x1, y1), (x2, y2), and (x3, y3) are given by:
G(X, Y) = [ (x1 + x2 + x3) ÷ 3 , (y1 + y2 + y3) ÷ 3 ]
Calculations:
⇒ Comparing the x-coordinate of the centroid:
⇒ 4 = (x + 5 + 2) ÷ 3
⇒ 12 = x + 7
⇒ x = 12 − 7
⇒ x = 5
⇒ Comparing the y-coordinate of the centroid:
⇒ 2 = (y − 1 + 6) ÷ 3
⇒ 6 = y + 5
⇒ y = 6 − 5
⇒ y = 1
⇒ The coordinates of vertex P are (5, 1).
∴ The correct answer is (5, 1).
Additional Information
Centroid of a Triangle
The centroid is the point of intersection of the medians of a triangle. It divides each median in a 2:1 ratio. Formula: G(X, Y) = [(x1 + x2 + x3) ÷ 3, (y1 + y2 + y3) ÷ 3].
Incenter of a Triangle
The incenter is the point of intersection of the internal angle bisectors. Coordinates: I(X, Y) = [(ax1 + bx2 + cx3) ÷ (a + b + c), (ay1 + by2 + cy3) ÷ (a + b + c)], where a, b, and c are side lengths.
Circumcenter of a Triangle
The circumcenter is the point where the perpendicular bisectors of the sides intersect. It is equidistant from all three vertices of the triangle.
Orthocenter of a Triangle
The orthocenter is the point where all three altitudes of the triangle intersect. For a right-angled triangle, the orthocenter lies at the vertex containing the right angle.