Answer:
b=6
Explanation:
modul of the vector AB= sqrt((b-2)^2+(3-1)^2)= sqrt (b^2-4b+8). It is the length of the side AB
modul of the vector BC is equal to sqrt ((b-5)^2+(-2)^2)= sqrt (b^2-10b+29)
modul of the vector AC is sqrt ((5-2)^2+(5-1)^2)= 5
squared modul of AB + squared modul of BC = squared modul of the vector AC.
b^2-4b+8+b^2-10b+29=25
2b^2-14b+12=0
b^2-7b+6=0
b=1 b=6
b>5, s0 b=6