Question

PREPARE E RESOLVA OS SISTEMAS PELO MÉTODO DE ADIÇÃO:
a) { 2x+5y=20
3x+4y=23


b) { 7x-3y=-16
5x+4y=7

Answer 1

a)  2x+5y=20(3)
     3x+4y=23(-2)


 6x+15y=60
-6x-8y= - 46
     7Y =14  ==> Y = 2
=================================================
2x + 5y = 20 ==> 2x = 20 -5(2)

2x = 20 -10 ==> 2x = 10 ==> x = 5
=======================================

b) { 7x-3y=-16(4)
      5x+4y=7(3)

28x-12y= -64
15x+12y= 21
   43x = - 43 ==> x = - 1

========================================

5x+4y=7==> 4y = 7 - 5x

4y = 7 -5(-1)

4y = 7 + 5

y = 3

Answer 2

A)
{2x+5y=20 (-4)
{3x+4y=23 (5)

-8x-20y=-80
15x+20y=115

7x=35
x=35÷7
x=5

2x+5y=20
10+5y=20
5y=20-10
5y=10
y=10÷5
y=2

B)
{7x-3y=-16 (4)
{5x+4y=7 (3)

28x-12y=-64
15x+12y=21

43x=-43
x=43÷(-43)
x=-1

5x+4y=7
5+4y=7
4y=7-5
4y=2
y=2÷4
y=0,5