Question

resolva os sistemas:
a){ x +y= 15
{x-y =3
b){ 2x+y=27
{3x-4y=2

Answer 1

A)
x+y=15. . 9+y=15
x-y=3. . y=6
2x=18.
x=9.
B)
2x+y=27. .3×10-4y=2
3x-4y=2. .-4y=-28
8x+4y=108. .y=7
3x-4y=2.
11x=110.
x=10.

Answer 2

A)
x + y = 15
x - y = 3

x = 15 - y
15 - y - y = 3
15 - 2y = 3
- 2y = 3 - 15
- 2y = - 12
y = - 12 ÷ - 2
y = 6

x + 6 = 15
x = 15 - 6
x = 9

S= {9; 6}

B)
2x + y = 27
3x - 4y = 2

y = 27 - 2x

3x - (27 - 2x) = 2
3x - 27 + 2x = 2
5x - 27 = 2
5x = 2 + 27
5x = 29
x = 29 ÷ 5
x = 5,8

2. 5,8 + y = 27
10,16 + y = 27
y = 27 - 10,16
y = 16,84

S= {5,8; 16,84}