5x-y=45
-x+4y=-28
this is not two, its only one problem...
how do you solve this algebra problem...?
2009-04-10 4:31 pm
回答 (8)
2009-04-10 4:38 pm
✔ 最佳答案
Hi,5x - y = 45
-x + 4y = -28
Multiply the second equation by 5. then add the equations and solve.
5x - y = 45
5(-x + 4y = -28)
5x - y = 45
-5x + 20y = -140
-------------------------
19y = -95
y = -5
If y = -5 and 5x - y = 45, then
5x - y = 45
5x - (-5) = 45
5x + 5 = 45
5x = 40
x = 8
(8, -5) <==ANSWER
I hope that helps!! :-)
2009-04-10 4:37 pm
take the first equation
5x - y = 45 that means 5x -45 = y
apply this value of y in second equation
-x +4 (5x-45) = -28
expanding
-x +20x -180 = -28
19x -180 +28 = 0
19x -152 = 0
19x = 152
x = 8
apply this value of x in first equation
5 (8) - y = 45
ie 40 - y = 45
y = 40-45 = -5
values are x = 8 and y = - 5
5x - y = 45 that means 5x -45 = y
apply this value of y in second equation
-x +4 (5x-45) = -28
expanding
-x +20x -180 = -28
19x -180 +28 = 0
19x -152 = 0
19x = 152
x = 8
apply this value of x in first equation
5 (8) - y = 45
ie 40 - y = 45
y = 40-45 = -5
values are x = 8 and y = - 5
2009-04-10 4:36 pm
x= 8
and
y= -5
and
y= -5
2009-04-10 4:34 pm
////////////
y=-5,x=8
y=-5,x=8
2009-04-10 5:02 pm
k so you multiply everything in the second equation by 5. then you make it a addition problem.
5x-y=45
+-5x+20y=-140 the answer is 19y=-95 notice how the x dropped out.
now you divide the -95 by 19. that is -5. that means y=-5
now you enter -5 as y in one of the original problems
-x+4(-5)=-28 now just do calculations to narrow it down. 4(-5)=-20
-x+-20=-28 add 20 to both sides
-x=-8 now divide both sides by -1
x=8 so the answer is......... x=8 y= -5
5x-y=45
+-5x+20y=-140 the answer is 19y=-95 notice how the x dropped out.
now you divide the -95 by 19. that is -5. that means y=-5
now you enter -5 as y in one of the original problems
-x+4(-5)=-28 now just do calculations to narrow it down. 4(-5)=-20
-x+-20=-28 add 20 to both sides
-x=-8 now divide both sides by -1
x=8 so the answer is......... x=8 y= -5
參考: math class
2009-04-10 4:46 pm
5x - y = 45 (solve by using substitution)
-x + 4y = -28
-x + 4y = -28
x = 4y + 28
5x - y = 45
5(4y + 28) - y = 45
20y + 140 - y = 45
20y - y = 45 - 140
19y = -95
y = -95/19
y = -5
-x + 4y = -28
-x + 4(-5) = -28
-x = -28 + 20
x = -8/-1
x = 8
∴ x = 8 , y = -5
-x + 4y = -28
-x + 4y = -28
x = 4y + 28
5x - y = 45
5(4y + 28) - y = 45
20y + 140 - y = 45
20y - y = 45 - 140
19y = -95
y = -95/19
y = -5
-x + 4y = -28
-x + 4(-5) = -28
-x = -28 + 20
x = -8/-1
x = 8
∴ x = 8 , y = -5
2009-04-10 4:38 pm
5x - y = 45
-x + 4y = -28
The second equation has a 4y in it. Multiply the first equation by 4, then add it to the second equation.
20x - 4y = 180
-x + 4y = -28
--------------------
19x = 152
The y terms have been eliminated, so you can solve for x.
x = 152/19 = 8
Now put the value of x into one of the equations.
5(8) - y = 45
y = -5
-x + 4y = -28
The second equation has a 4y in it. Multiply the first equation by 4, then add it to the second equation.
20x - 4y = 180
-x + 4y = -28
--------------------
19x = 152
The y terms have been eliminated, so you can solve for x.
x = 152/19 = 8
Now put the value of x into one of the equations.
5(8) - y = 45
y = -5
2009-04-10 4:36 pm
5x-y = 45
y = 5x - 45
sub y s value in the 2nd equation.....
y = 5x - 45
sub y s value in the 2nd equation.....
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