Let A, B, C and D represent the points (-7, -3), (5, 10), (15, 8) and (3, -5) respectively.
Using the distance formula d=√(x2−x1)2+(y2−y1)2, we find
AB2=(5+7)2+(10+3)2=122+132=144+169=313
BC2=(15−5)2+(8−10)2=102+(−2)2=100+4=104
CD2=(3−15)2+(−5,−8)2=(−12)2+(−13)2=144+169=313
DA2=(3+7)2+(−5+3)2=102+(−2)2=100+4=104
So, AB=CD=√313 and BC=DA=√104
i.e., The opposite sides are equal. Hence ABCD is a parallelogram.