Respuesta :

anika87

Step-by-step explanation:

pythagoras theorem: c²=a²+b²

Where c= longest side of a right angle triangle

AB= 6+r = c

AD= 12 =a

CD= r =b

(6+r)² = 12²+ r²

36+12r+r² =144 +r²

12r+r²-r²=144-36

12r=108

r= 108/12

r=9