anonymous
  • anonymous
HELP ME WITH THIS PROBLEM PLEASE! Solve with substitution method. 5x – y = –1 7x – 3y = 13
Algebra
  • Stacey Warren - Expert brainly.com
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SOLVED
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katieb
  • katieb
I got my questions answered at brainly.com in under 10 minutes. Go to brainly.com now for free help!
anonymous
  • anonymous
5x – y = –1 7x – 3y = 13 chose top or bottom equation in my case i chose top. SOlve for y or x i chose y since it looks simplest 5x-y=-1 -y=-1-5x subtract 5x from both sides. y=1+5x multiply by -1 both sides to get rid of that negative. WITH ME SO FAR? now you substitude 1+5x into the y variable into either top or bottom equation. I chose top equation again 5x- (1+5x)=-1 Now solve for x 5x-1-5x=-1 distribute the - -1=-1 from what i can see is that these 2 equations overlap. Meanin infinite many solutions. Or I did it wrong :P
anonymous
  • anonymous
I did it wrong somewhere let me check dbl check
anonymous
  • anonymous
Thank you so much<333

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anonymous
  • anonymous
Oh okay
anonymous
  • anonymous
mathway says y=-9 and x=-2
anonymous
  • anonymous
I know :P
anonymous
  • anonymous
I think where i went wrong was that i chose to plug in (1+5x) into top equation. That is wrong. I think i should plug it into bottom equation lets try that (1+5x) 7x – 3y = 13 7x – 3(1+5x) = 13 plugged in 7x-3-15x=13 distributed the -3 8x-3=13 added like term the 7x and - 15x = 8x 8x=16 add 3 to both sides x=2 divide both sides by 8 YAY x=2 we more than half way done.
anonymous
  • anonymous
I thought x is -2?
anonymous
  • anonymous
(1+5x) 7x – 3y = 13 7x – 3(1+5x) = 13 plugged in 7x-3-15x=13 distributed the -3 -8x-3=13 added like term the 7x and - 15x = -8x HERE ^ ^ :( forgot the - sign -8x=16 add 3 to both sides x=-2 divide both sides by -8 YAY x=-2 we more than half way done.
anonymous
  • anonymous
Ok now for sure knowing x=-2 you plug it into bottom or top equation and solve for y OR here is a neat trick you know from the first step how we figured out that y=(1+5x) when we solved for the top equation? Well use that y=1+5(-2) y=1-10 = -9
anonymous
  • anonymous
sorry i made so many little careless mistakes
anonymous
  • anonymous
It's okay, at least you helped and went back to fix them :) Do you mind helping me with 2 more questions? :)))
anonymous
  • anonymous
Ask away brb in less than 10 minutes
anonymous
  • anonymous
Solve with elimination 2x + 9y = 4 3x + 7y = –7 I know that if I multiply the first eaution by -3 i'll get -6x for the fist term and if I multiply the second equation by 2 i'll get 6x for the first term. then I add them right? After that I'm lost lol
anonymous
  • anonymous
after adding them i got y=2. now what? lol
anonymous
  • anonymous
Well elimination means you wanna eliminate one of the xs or ys. ANd you do that by adding a multiple of top equation to bottom :) I'll explain more
anonymous
  • anonymous
2x + 9y = 4 eq 1 3x + 7y = –7 eq 2 We wanna eliminate the 3x in eq 2. By adding a multiple of eq 1 to it 3+2*X=0 solve for X notice it is capital X so dont confuse for x 2X=-3 subtract 3 from both sides X=-3/2 divide by 2 both sides so now you have that multiple that you should multiply by So it should be eq2+eq1*(-3/2) eq1*-3/2 looks like this (-3/2)* (2x + 9y = 4) = -3x-(27/2)y=-6 now lets add. Imma do it by putting them on top of eachother 3x + 7y = –7 eq 2 -3x-(27/2)y=-6 eq1*(-1/3) 0 -(13/2)y=-13 as you can see we eliminated a x -(13/2)y=-13 what you can do now is y=-13/-(13/2) divide by -(13/2) y=2 --- this is your original--- 2x + 9y = 4 3x + 7y = –7 ---after elimination---- 2x + 9y = 4 -(13/2)y=-13 or 2x + 9y = 4 y=2 and you are done. Unless they ask you to back substitude y=2 into top equation.
anonymous
  • anonymous
I dont need the value of x?
anonymous
  • anonymous
Wait I'm condused, Did I do mine wrong?
anonymous
  • anonymous
oh wait i think you do but all you have to do is back substitude :) since you know y=2 THen 2x+9y=4 2x+9*2=4 plugged in the 2 at y. Now just solve :)
anonymous
  • anonymous
Oh okay, Thank you :)
anonymous
  • anonymous
De nada
anonymous
  • anonymous
btw i dbld checkd and y is indeed 2 :D hope you can do the rest.
anonymous
  • anonymous
Okay, Last one I promise. lol x – 2y < 18 4x + y > –5 Solve by graphing method
anonymous
  • anonymous
:) i'm sorry for being such a pain lol
anonymous
  • anonymous
do you know how to graph y=mx+b type of lines?
anonymous
  • anonymous
yeah, I think. I dont remember...
anonymous
  • anonymous
ookay wait. for the first equation i isolate y by subtracting x and divideing by -2? then i get -2/1 and -9?
anonymous
  • anonymous
Nevermind, I'm dumb. lol I dont know if I did it right.
anonymous
  • anonymous
x – 2y < 18 4x + y > –5 first we will convert both in terms of y x – 2y < 18 -2y<18-x subtract x y>-9+1/2x the sign flipped cuzz it is a rule of dividing or multiply by a - which we did cuzz we divided by -2 y>1/2x-9 rearange to y=mx+b mode but replace = with > ----- 4x + y > –5 y>-5-4x subtract 4x y>-4x-5 rearrange. so you have y>1/2x-9 y>-4x-5
anonymous
  • anonymous
|dw:1377647920217:dw|
anonymous
  • anonymous
|dw:1377648141198:dw| since you have y>... y>... the > means shade above. Or that is how i interpret it. I am shading for the line that crosses the -5
anonymous
  • anonymous
|dw:1377648212010:dw|
anonymous
  • anonymous
Now shade for line that crosses -9 here is a computer generated one http://www4b.wolframalpha.com/Calculate/MSP/MSP401fcde47224899g6300005f59dc16g8ad89a0?MSPStoreType=image/gif&s=29&w=200.&h=196.&cdf=Coordinates&cdf=Tooltips
anonymous
  • anonymous
is that -3,-9 or -9,-3?
anonymous
  • anonymous
-9 and - 5 sorry i suck at drawing :(
anonymous
  • anonymous
lol its okay. the shading is kinda messy too. Is it shading above or below for the first and second equation? && their both dashed right?
anonymous
  • anonymous
Yes dashed :D and both are above :D |dw:1377648547329:dw|
anonymous
  • anonymous
that is region that should be shaded where they intersect
anonymous
  • anonymous
THANK YOU THANK YOU THANK YOU SOOOOO MUCH!!<3333333333
anonymous
  • anonymous
YOURE THE BEST!!!!

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