Question

Use the substitution method to solve the linear system.
4×- 7y = 20
X- 3y = 10

Answer 1

The second equation can also be written as
X= 10+3y
Substitute the x in the first equation with 10+3y

4 ( 10+3y) -7y= 20
40+12y-7y= 20
5y= -20
Y = -4

If y = -4
Then using second equation, plug in y
X - 3 (-4) = 10
X+ 12 = 10
X= -2

Answer 2

y = -4

x = -2

Explanation:

4x - 7y = 20 Eq. 1

x - 3y = 10 Eq. 2

from the Eq. 2:

x = 10 + 3y Eq. 3

substituying Eq. 3 in the Eq. 1

4(10+3y) - 7y = 20

(4*10 + 4*3y) - 7y = 20

(40 + 12y) - 7y = 20

12y - 7y = 20 40

5y = -20

y = 5/-20

y = -4

from the eq. 3:

x = 10 + 3y

x = 10 + 3*-4

x = 10 - 12

x = -2

Check:

from te eq. 1:

4x - 7y = 20

4*-2 - 7*-4 = 20

-8 + 28 = 20