Select the appropriate response. An isosceles triangle has vertices at (1,1) and (3, 3). Which of the following could be
the coordinates of the third vertex?
A. (2.1)
B. (3.2)
C. (4,1)
D. (5,1)
Choose

D. (5,1)

Step-by-step explanation:

Because it is an isosceles triangle, the next point we choose must result in two sides with the same length. This means that either the two new sides are equal, or that one of the new sides is equal to the original side. If we wanted both of the new sides to be equal, they would have to be equal distance from the new point and one of the points of the original line. However, none of the options result in both new lines being the same length.

(2,1) would result in one new length being 1 unit long (2-1 x-coordinates) and the other being square root 5 (distance from point 2,1 to point 3,3 minus both coordinates and use Pythagoras). Points 3,2 and 4,1 yield the same result: Length 1=1 unit length 2=square root 5. Length 1 = 3 unit, length 2 = square root 5.

Therefore we are looking for a point which instead yields one length which is the same length as the original. The original length was 2^2 + 2^2 = c^2 = square root 8.

If we try the point 5,1 then we get two lengths of 4 and square root 8, it forms a isosceles triangle whose base line is parallel to the x-axis.

Sorry is my explanation was confusing, it's much easier to try and draw it on a grid and visualize it. Basically the overall idea is to test the side values you get by finding the distance between the points and going with the option which results in two sides with the same length.

Hope this helped!