Respuesta :

line AC=21cm
line AB=20cm

substitute values into the pythagorean theorem to find the hypotenuse
(a^2 + b^2 = c^2):

(21)^2 + (20)^2 = c^2
441 + 400 = c^2
841 = c^2
29=c

so, line BC = 29cm

hope this was helpful :)