Which point is which?

Geometry Level 3

ΔOPQ has vertices O(0, 0), P(12.6, 0), and Q(3, 7.2).

Lying in the interior of ΔOPQ are the following points:

Point 1: (3, 4),
Point 2: (4.2, 2.8),
Point 3: (5.2, 2.4), and
Point 4: (6.3, 1.6).

Write the four-digit number in which the first digit corresponds to the centroid,
the second digit corresponds to the circumcenter,
the third digit corresponds to the incenter,
and the fourth digit corresponds to the orthocenter of ΔOPQ.


The answer is 3421.

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1 solution

Mark Jones
Jan 22, 2018

The centroid is the ordered pair (average(x), average(y)), or (5.2, 2.4)... point 3. The circumcenter is the point of concurrency of the perpendicular bisectors of each side. The perpendicular bisector of O P \overline{OP} is the line x = 6.3, on which point 4 lies. The incenter of a triangle that's not isosceles will not fall on the Euler line of the triangle, the the only one of the four points not colinear with the others is point 2. The orthocenter is the point of concurrency of the altitudes. The altitude on O P \overline{OP} through Q is the line x = 3, on which point 1 lies. The number is 3421.

I think the problem would be even better if no info beyond the picture was available, but that's probably just me.

Marta Reece - 3 years, 4 months ago

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