Math question! Solve by substitution 2x-4y=7 4x+y=5?
回答 (4)
2016-06-17 6:45 pm
Solve by SUBSTITUTION :
2x - 4y = 7 ...... [1]
4x + y = 5 ...... [2]
From [2] :
y = 5 - 4x ...... [3]
Substitute [3] into [1] :
2x - 4(5 - 4x) = 7
2x - 20 + 16x = 7
2x + 16x = 7 + 20
18x = 27
x = 27/18
x = 1.5
Put x = 1.5 into [3] :
y = 5 - 4(1.5)
y = 5 - 6
y = -1
Ans: x = 1.5, y = -1
2x - 4y = 7 ...... [1]
4x + y = 5 ...... [2]
From [2] :
y = 5 - 4x ...... [3]
Substitute [3] into [1] :
2x - 4(5 - 4x) = 7
2x - 20 + 16x = 7
2x + 16x = 7 + 20
18x = 27
x = 27/18
x = 1.5
Put x = 1.5 into [3] :
y = 5 - 4(1.5)
y = 5 - 6
y = -1
Ans: x = 1.5, y = -1
2016-06-17 7:20 pm
[ 7 + 4y ] = 2x
14 + 8y = 4x
14 + 8y + y = 5
9y = - 9
y = - 1
4x = 6
x = 3/2
x = 3/2 , y = - 1
14 + 8y = 4x
14 + 8y + y = 5
9y = - 9
y = - 1
4x = 6
x = 3/2
x = 3/2 , y = - 1
2016-06-17 6:18 pm
4x + y = 5
y = 5 - 4x
2x -4y = 7
2x -4(5 - 4x) = 7
2x -20 + 16x = 7
18x = 27
x = 27/18 = 3/2
y = 5 - 4x
2x -4y = 7
2x -4(5 - 4x) = 7
2x -20 + 16x = 7
18x = 27
x = 27/18 = 3/2
2016-06-17 6:17 pm
If you make one of the variables as like terms you can eliminate them by substitution.
so 2x - 4y=7 and 16x+4y=20,
bring y to the left hand side
4y = 2x - 7 and 4y = 20 -16
2x - 7 = 20 - 16x
14x = = 27
x = 1.5
put that in second equation to get y
y = -1
so 2x - 4y=7 and 16x+4y=20,
bring y to the left hand side
4y = 2x - 7 and 4y = 20 -16
2x - 7 = 20 - 16x
14x = = 27
x = 1.5
put that in second equation to get y
y = -1
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