algebra 2 math homework help please?

you have to solve for y and x by substitution...

1) 5x+4y=-9

x-3y=21

>>

5(21+3y)+4y=-9

105+15y+4y=-9

105+19y=-9

19y=-114

y=-114/19

y=-6

then..

x-3y=21

x-3(-6)=21

x+18=21

x=21-18

x=3

2)2x+y=8

-2x+5y=16

2x+y=8

y=8-2x

so..

-2x+5(8-2x)=16

-2x+40-10x=16

-12x=-24

x=-24/-12

x=2

then...

y=8-2(2)

y=4

3)8x+3y=8

-8x+y=-8

y=8x-8

so..

8x+3(8x-8)=8

8x+24x-24=8

32x=32

x=1

then...

y=8(1)-8

y=0

4)4x-2y=-24

-3-7y=18 (i think an x is missing.. but if not, its ok)

y=3

so...

4x-2(3)=-24

4x-6=-24

4x=-24+6

4x=-18

x=-4.5

5)-3x+y=-2

-9x+3y=-8

x=(-2-y)/-3

so...

-9(-2-y)/-3+3y=-8

-3(-2-y)+3y=-8

6+3y+3y=-8

6y=-14

y=-2.3333

then...

x=[-2-(-2.333)]/-3

x=0

i 'm not sure with my answers. i might have commited some errors...

but that's how you do it.

I'll walk you through the first, then you should have no problem with the rest.

Take one of your equations, and move a variable to one side of the equals sign so it is by itself. It only works if the other equation has this variable also, like this:

5x + 4y = -9 Subtract 4y from each side to move it to the right

5x = -9 -4y

Lose the 5 by dividing BOTH sides by 5

5x/5 = ( -9 - 4y) /5

5x/5 becomes just x.

x = ( -9 - 4y) /5

Now plug in what x is equal to in the other problem like this.

x - 3y = 21 and replace x

(-9 - 4y)/5 - 3y = 21

Now solve for y!

(-9/5) - (4/5)y - 3y = 21

Let me know if you need help with this.

The method is to find x in terms of y (or vice versa) from one of the equations and substitute into the other equation. Example problem 1)

Given 5x+4y=-9 and x-3y=21

Solve second equation for x -> x=3y+21

Substitute into first equation -> 5(3y+21)+4y=-9 and solve as follows

15y+105+4y=-9

19y=-114

y=-114/19

Then substitute the value for y into one of the other equations and solved for x.

1)

a) 5x+4y=-9

b) x-3y=21

b) x-3y = 21

so x = 21+3y

thus put b into a

a)

5x+4y = -9

-> 5(21+3y) + 4y = -9

-> 105+15y+4y = -9

19y = -114

y = -6

plug in y (-6) for equation b to solve for x

x-3y=21

x-3(-6)=21

x+18=21

x = 3

might be careless mistakes

I love algebra 2. just solve for x or y and then plug it into the second equation.

ex.

1) 5x+4y=-9

x-3y=21

x=(-9-4y)/5 and then plug it into the 2nd equation and solve

pretty sure that you solve for x or y first, then put that answer in the other equation.

like 1) x-3y=21

x=3y+21

so now that you know what x is, you put it in the other equation

5x+4y=9

5(3y+21)+4y=9

then just solve it for y

thats my guess lol, hope it helps

well... to do the first question move the -3y to the right side so the equation will look like: X=3y+21 and you sub that for X in the first equation so it looks like 5(3y+21)+4y and solve for y. once you get y sub it in and get x. you do the rest of the problems similarly. isolate one variable and sub it in. i hope i helped a little bit.

1) 5x+4y=-9

x-3y=21

x=21+3y

5(21+3y) + 4y = -9

105 + 15y + 4y = -9

19y = -116

y= 12.8888

x= 21+3y

x=21+3*12.8

x=59.6666

1) 5x+4y=9

5x-15y=105

work it out from there.

OMG that looks super hard and is confusing sry i couldnt help wish i could!!