What is the perimeter, in cm, of quadrilateral $ABCD$ if $\overline{AB} \perp \overline{BC}$, $\overline{DC} \perp \overline{BC}$, $AB=9$ cm, $DC=4$ cm, and $BC=12$ cm?
A 9 B
12
D 4 C
Let A = (0,0)
Let B= (9,0)
Let C = ( 9, -12)
Let D = (5, -12)
We know three sides......we just need to find AD = sqrt [ ( 0 - 5)^2 + ( -12 - 0)^2 ] =
sqrt [ (-5)^2 + (-12)^2 ] =
sqrt [ 25 + 144 ] =
sqrt [ 169] =
13
So.....the perimeter is 9 + 12 + 4 + 13 = 38 cm