16 September, 01:49

# 4x + 5y = - 28-4x - 7y = 28

+4
1. 16 September, 05:28
0
Answer: x = - 7, y = 0

Step-by-step explanation:

4x + 5y = - 28 (1)

-4x - 7y = 28 (2)

from equation (1)

4x + 5y = - 28

to make 'x' the subject of formula

4x = - 28 - 5y

divide both sides by 4

x = (-28 - 5y) / 4 (3)

substituting equation (3) into (2)

-4 [ ( - 28 - 5y) / 4] - 7y = 28

28 + 5y - 7y = 28

-2y = 28 - 28

-2y = 0

y = 0

substitute y = 0 into equation (1)

4x + 5 (0) = - 28

4x + 0 = - 28

4x = - 28

divide both sides by 4

4x/4 = - 28/4

x = - 7

Therefore, x = - 7, y = 0
2. 16 September, 05:43
0
x = - 7, y = 0

Step-by-step explanation:

Solve the following system:

{4 x + 5 y = - 28 | (equation 1)

-4 x - 7 y = 28 | (equation 2)

Add equation 1 to equation 2:

{4 x + 5 y = - 28 | (equation 1)

0 x - 2 y = 0 | (equation 2)

Divide equation 2 by 2:

{4 x + 5 y = - 28 | (equation 1)

0 x - y = 0 | (equation 2)

Multiply equation 2 by - 1:

{4 x + 5 y = - 28 | (equation 1)

0 x+y = 0 | (equation 2)

Subtract 5 * (equation 2) from equation 1:

{4 x+0 y = - 28 | (equation 1)

0 x+y = 0 | (equation 2)

Divide equation 1 by 4:

{x+0 y = - 7 | (equation 1)

0 x+y = 0 | (equation 2)

Collect results:

Answer: {x = - 7, y = 0