Geometry Question

[gmatdelhi]

ABC is a triangle with side AB = 15, BC = 9 and CA = 12. What is the measure of angle C?

[selango]

90

AB^2=BC^2+AC^2

[jeremy8]

If you look at the measures given to you for this triangle: 9,12,15, you can see that they are multiples of a 3,4,5 triangle, a classic right triangle measurement, whose sides obey the pythagorean theorem 3^2+4^2=5^2, which is true of any multiple of these measures (6,8,10....12,16,20...etc....)

If you draw a right triangle ABC using AB=15 as the hypothenuse since it is the longest side, and AC and BC as the two other sides, you can see that angle C necessarily corresponds to the 90 degree angle of this right triangle.