To find the length of the triangle first find the two coordinates with a common x coordinate, (1,-1) and (1,2). Now find the difference between their y coordinates, -1 and 2. This means that the length of the triangle is 3.
To find the width of the triangle first find the two coordinates with a common y coordinate, (-3,-1) and (1,-1). Now find the difference between their x coordinates, -3 and 1. This means that the width of the triangle is 4.
By Pythagoras' theorem, we know that

. Inserting our newfound values into this equation, we an find thelength of the hypotenuse:

Therefore, your answer is D0 5. To visualise this question better, you can plot the points on a graph.