Question

solve system of equations using substitution:
5x+6y+8=0
3x-2y+16=0 Please show work (:

Answer 1

er why substitution. looks like subtraction would be wayyy easier.

Answer 2

has to be substitution, thats the way it says to solve it! ):

Answer 3

substitue substituion with subtraction :)

Answer 4

substitute*

Answer 5

multiply the second equation by 3 and subtract it from the first then solve for x (that's how id do it)

Answer 6

I have to do substitution. Actually, I got an answer to this but it didn't look right. So thats why I'm asking about it.

Answer 7

so you get 9x+6y+48 and subtracting this from 5x+6y+8 = 0 and you get -4x-40=0 so you get x =10

Answer 8

sorry that first equation should say =0

Answer 9

but it's got to be substitution. I have to show my work.

Answer 10

kk. substitute 6y (solve from 3 times the second equation) into the first equation

Answer 11

6y=48-9x

Answer 12

where did you get the 48 and nine from??

Answer 13

i multiplied the whole equation by three

Answer 14

why?

Answer 15

it makes it easier so you dont have to divide anything
it's also legal because i did it to both sides of the equation

Answer 16

Alright, but you still have to divide tot get y alone

Answer 17

you can but it's easier and still technically substitution. I copied the problem down work 6y =48+9x

Answer 18

but wouldn't something be negative?

Answer 19

nevermind

Answer 20

nope the negatives cancel out on the second equation when you solve for y

Answer 21

or 6y

Answer 22

alright, so i got y=9/6x+8

Answer 23

so you end up with 5x + 48+9x+8=0 after subbing in 6y

Answer 24

what?

Answer 25

that looks right

Answer 26

how? if you use what i did to substitute for y then there can't be 48 or nine in it.

Answer 27

i did it differently than you, instead of solving for y i solved for 6y and substitute what 6y is equal to in terms of x according the the second equation into the first equation

Answer 28

either way is valid

Answer 29

you need to do it schuyler's way if you want to work with whole numbers. else you get nasty fractions. Which is why you should use subtraction in these instances.

Answer 30

Yeah but I can't I have to show work for subsitition. and I don't understand schuyler's way at all

Answer 31

ight check this out yo, homz.

Answer 32

it's okay if you don't understand yet. Just think about it though. You don't necessarily have to solve for just the variable. you can solve for whatever you like. 6y for example instead of y. as long as you follow the rules of algebra you'll get a valid answer, and with enough practice you'll get it

Answer 33

if you multiply the second equation by 3. Everything gets trippled. so instead of 3x-2y+16, you get 9x-6y+48

Answer 34

alrighttt.... i guess I kind of get it. so you replace 6y with what the other 6y equals?

Answer 35

so now your system looksalikedis. 5x+6y+8=0
9x-6y+48= 0

Answer 36

now when your ststem lookalikedat, you can add everything together :O (so this means you'll get 14x +nothing because +6+-6=0 +54 because 48+8 = 54
leaving you with 14x+54=0

Answer 37

with 14x+54 = 0 you subtract the 54 over to the left, leaving you with 14x = -54, then divide -54 by 14x, leaving you with - 4. So X now = -4!!!!! now we can substitute.

Answer 38

now I'm even more confused. Then I was before. Thanks for trying though.

Answer 39

aw.

Answer 40

okay! I shall devise a plan.

Answer 41

alright. kind of sounds a bit devious... (:

Answer 42

what's 56 divided by 14?

Answer 43

4

Answer 44

but it should be -4 when you subtract 54 to the right side

Answer 45

alright I think I got it! is x= -4 !

Answer 46

YES.

Answer 47

I drew you a big picture :) want it or do you understand?

Answer 48

but now i don't know how to do the next part

Answer 49

HOKAY. Just wait :P

Answer 50

alrighty

Answer 51

oh crap
I can't send it
okay I'll explain it

Answer 52

you know we got x=-4 right?

Answer 53

YES!

Answer 54

(:

Answer 55

so going back to the equations. You started with 5x+6y+8 = 0 right?

Answer 56

yep

Answer 57

:o but you know what x is!! so it's really 5 TIMES -4 +6y+8 = 0

Answer 58

:O!!!!!!!!!!!!!!

Answer 59

I GOT IT! I think! x=-4 and y=14

Answer 60

?

Answer 61

well 5 x -4 is -20. -20 +8 is -12 :P

Answer 62

so if you have 6y-12 = 0 what do you do?

Answer 63

wait why are you using that problem? shouldn't you be using 6y=9x+48?

Answer 64

noooooo. You should be plugging it back into the ORIGINAL equation

Answer 65

HOWEVER

Answer 66

Oooooohhh. weellll theeen never mind!

Answer 67

9(-4) = -36 +48 = 12 all the same ;P

Answer 68

so you have 6y-12 = 0. we want to add 12 to both sides of the =

Answer 69

wait so is y=2

Answer 70

yes y is 2 but i meant to say you are subtracting 12 from both sides

Answer 71

negative 2!!!

Answer 72

its fine! I totally got it now!

Answer 73

THanks

Answer 74

it's -2!!! lol sorry

Answer 75

glad I could help!

Answer 76

wait! Why is it negative if you add 12?

Answer 77

because I fluttere dup. you're supposed to subtract 12

Answer 78

why its a negative 12?

Answer 79

6y+12 = 0 , so you -12 to get 6y= -12. then -12/6 = -2

Answer 80

no because -4 x 5 = -20 + 8 = -12

Answer 81

Multiply the first equation by 2. You now have two equations where the constant is 16. Equate the x and y terms in the first equation to the x and y terms in the second equation and solve for y.\[10x+12y\text{=}3x-2y \]\[y=-\frac{x}{2} \]Plug y into the second equation and solve for x.