X+5y=21

x+3y=11

3x+y=13

5x+2y=7

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- Feb 11th 2009, 05:52 PMthebesta1May someone solve this equations for me?
X+5y=21

x+3y=11

3x+y=13

5x+2y=7 - Feb 11th 2009, 06:02 PMTheMasterMind
x+5y=21

x+3y=11

x=21-5y (isolate x)

sub the value of x to 2nd equation to solve for y

21-5y+3y=11

-2y=-10

y=5

substitute the value of y into the other equation to solve for x

x+5(5)=21

x+25=21

x=-4

Do you see what I did? Now follow the same method for solving the second one and show me what you get - Feb 14th 2009, 06:44 PMaidan
from this

1x + 5y = 21

1x + 3y = 11

1 5

1 3

1*3 - 1*5 = 3-5 = -2

the determinant of the equation

Then find the determinant of a replacement:

replace the constants of the variable x:

21 5

11 3

21*3 - 11-5 = 63 - 55 = 8

Then divide this determinant with the system determinant:

8 / -2 = -4

Thus x = -4

Then do the same and replace the constant of y:

1 21

1 11

1*11 - 21*1 = 11 - 21 = -10

-10 / -4 = 2.5

thus y = 2.5