x/3=y/5=z/9=t
x/3=t deci x=3t
y/5=t deci y=5t
z/9=t deci z=9t
a) x+z-y=21
3t+9t-5t=21
7t=21 t=3 rezulta : x=3x3=9 ; y=5x3=15 ; z=9x3=27
b) (3t) la a doua+(5t) la a doua + (9t) la a doua =1035
9tpatrat + 25tpatrat+ 81tpatrat = 1035
tpatrat= 1035/115
t= radical din9
t=3 si asa mai departe