you did
D=(x2-x1)²+(y2-y1)²
it should be
D=[tex] \sqrt{(x_2-x_1)^2+(y_2-y_1)^2} [/tex]
and BC, you did (-4)²=-16, it should be equal to 4
if you do the math which is evaluate
A=(5,3)
B=(1,5)
C=(3,0)
AB=[tex] \sqrt{(1-5)^2+(5-3)^2}= 2\sqrt{5} [/tex]
BC=[tex] \sqrt{(3-1)^2+(0-5)^2}= \sqrt{29} [/tex]
CA=[tex] \sqrt{(5-3)^2+(3-0)^2}= \sqrt{13} [/tex]
add them to get total
