Answer:
Yes, it is a right triangle.
Explanation:
Look at the points:
(1, 1), (1,4)
(1,4), (4,4)
(4,4), (1,1)
Find the slope between each point: In respective order, the first one is undefined, the second one has a slope of zero, and the third has a slope of 1. Because undefined slope is completely vertical (parallel to the y axis, and the slope of 0 is completely horizontal (parallel to the x axis), they are perpendicular (as it is transitive since the x axis is perpendicular to the y axis). Therefore, we know that anything that is perpendicular created a right angles', and thus, the any triangle with a right angle is a right triangle.