Question

2x + y = 10
3y + x = 21

Answer 1

2x+ y = 10
y = 10 - 2x

3y + x = 21
3(10 - 2x) + x = 21
30 - 6x + x = 21
30 - 5x = 21
-5x = 21 - 30
-5x = -9
x = -9 / -5
x = 9/5

y = 10 - 2x
y = 10 - 2(9/5)
y = 10 - 18/5
y = 50/5 - 18/5
y = 32/5

Answer 2

- Usarei o metodo da soma:

2x + y = 10 
3y + x = 21

multiplica por -2 a eq. 2 e soma com a primeira.

2x + y = 10
-6y-2x = -42
___________________
-5y = -32
y = 32/5


achando x.

2x + y = 10
2x = 10 - 32/5
2x = 18/5
x = 18/10
x = 9/5