Question

calcule o valor de x-3y no sistema {x-y=5 {2x-y=10

Answer 1

x-y=5 
2x-y=10  
x-2x-y-(-y) = 5-10 
-x = -5 => x=5  
x-y=5 
-y=5-x 
y=0
x-3y = 5-3(0) = 5