AB²=(-3+7)²+(10-2)²=16+64=80 AB=√80=4√5
BC²=(9+3)²+(4-10)²=144+36=180 BC=√180=6√5
AC²=(9+7)²+(4-2)²=256+4=260
observam ca AB²+BC²=AC² rezulta ca triunghiul ABC este dreptunghic in B
Aria triunghiul ABC= 4√5×6√5/2=60
Adreptunghi ABCD=4√5×6√5=120 cm
consideram D(a,b)
(a+7)²=(9+3)²
a+7=12
a=5
(b-4)²=(2-10)²
b-4=-8 b=-4
D(5,-4)
