Respuesta :

Amy24680

A triangle always has 180 degrees so to find the missing number do:

21+17+a = 180

38+a=180

180-38=a

a= 42

the answer is 42


Swastik1998
According to Pythagoras theorem,

21^2 = 17^2 + a^2
=> a= √(21^2-17^2)
=√152 = 12.329