Question

A seamstress is making a decorative pillow and wants to sew lace around the trim. The pillow is in the shape of a triangle with vertices (7, 7) (10, 3) (7, 3). How many inches of lace will she need if each unit on the grid is one inch?

Answer 1

Use the distance formula in order to find the length of each side of the triangle. 

>(7, 7) & (10, 3)
√[(7-10)² + (7-3)²] = 5

>(10, 3) & (7, 3)
√[(10-7)² + (3-3)²] = 3

>(7, 7) & (7, 3)
√[(7-7)² + (7-3)²] = 4

Adding all lengths (or solving for perimeter), we have: 5 + 3 + 4 = 12 

The seamstress will need 12 inches of lace.