x+2y=72x-3y=-21?

Question

please help, its my math homework on systems of equations and i dont get it AT ALL!!!!! please help!!!!!

Answer 1

Problem:

x+2y = -21 (1)
72x - 3y = -21 (2)

First you need to solve for x in terms of y so this gives you:

x+2y = -21
x = -21 -2y (3)

Next you plug the x you just solved for into (2) from above:

72 * (-21 - 2y) -3y = -21

Then you use the distributive property and solve for y:

(72*-21) + (72*-2y) -3y = -21
-1512 -144y -3y = -21
-147y = 1491
y=(1491/-147) = -71/7

Next you plug that y value into (3) from above:

x = -21 -2*(-71/7) = -21 + 142/7= -147/7 + 142/7 = -5/7

x = -5/7
y = -71/7

Answer 2

x + 2y = -21
72x - 3y = -21

Multiply the first equation by 72
72x + 144y = -1512
72x - 3y = -21

Subtract:
0x +147y = -1491

Divide by 150
y = -10.14286

Substitute into the first equation
x + 2(-10.14286) = -21
x = -21 + 20.28571 = -0.71429

Check with the second equation:
72 (-0.71429) - 3 ( -10.14286) =
-51.42857 + 30.42857 = -21

Answer 3

ugly problem. The answer is -10.142857...

trick is to let x = -21 - 2y. when you plug that in you get

72(-21-2Y) - 3Y = -21

simplified is

-1512-147y = -21

so
-147y = -21 + 1512 = 1491

1491/-147 = what i said above. ugly ugly

Answer 4

x + 2y = 7
2x - 3y = - 21

3x + 6y = 21
4x - 6y = - 42-------ADD

7x = - 21
x = - 3

- 3 + 2y = 7
2y = 10
y = 5

Solution is x = - 3, y = 5