Question

Por metodo de sustitucion

3x + y = 2
4x - y = 4

Answer 1

x=(2-y)/3

sustituyendo en 2
4(2-y)/3=4
2-y=3
y=5

de 1
3x+5=2
x=-1

Answer 2

3x + y = 2 :entonces: 3x = 2 - y :entonces: x = (2-y) / 3

x = 2/3 - 1/3y

sustituyendo x:

4(2/3 - 1/3y) - y = 4/1*2/3 - 4/1*1/3y - y = 8/3 - 4/3y - y = 4

despejamos Y:

- 4/3y - y = - 4/3 - 3/3y = - 7/3y = 4 - 8/3 = 4/3

y = 4/3 / - 7/3 = - 12/21 = - 4/7

sustituyendo y:

3x + y = 3x + - 4/7 = 2

despejamos x:   

3x = 2 + 4/7 = 14/7 + 4/7 = 18/7
 
x = 18/7 / 3 = 18/21 = 6/7

comprobacion: 

3x + y = 2
3(6/7) + -4/7 = 18/7 - 4/7 = 14/7 = 2

4x - y - 4
4(6/7) - -4/7 = 24/7 + 4/7 = 28/7 = 4