posted by .

please help, I have a test tomorrow and i don't get this.

solve by substitution
1. y = x - 3
x + y = 5

2. 5x + 2y = 0
x - 3y =0

  • math -

    if y=x-3, then you have to plug it into the equation.
    for numb 1, y=x-3 so when you plug that in it makes the equation x+y=5 turns into x+x-3=5. then you solve by making the sides equal.

    you do this by x+x-3=5

  • math -

    I'm with Zava on the idea, but I think one of us dropped a sign along the way. And I'm not at all sure it wasn't me, so I'll check at the end. Dropped signs happen all the time.

    We have:

    x + y = 5

    but we're also given what y is: y = x - 3

    So we can just replace y in the equation with (x-3)

    x + y = 5

    x + (x-3) = 5

    2x - 3 = 5

    2x = 5 + 3

    2x = 8

    x = 4

    and since y = x -3

    y = 4 - 3 = 1


    y = x - 3
    1 = 4 - 3 - OK

    x + y = 5
    4 + 1 = 5 - OK

    The second one is a leetle trickiersince you''ll have to make one of the equations work for the substitution

    x - 3y = 0

    -> x = 3y --- that's the one we'll use!

    5x + 2y = 0

    5(3y) + 2y = 0

    17y = 0 -> y = 0.

    No that's not a mistake. The only answer is if x and y are both zero!

Respond to this Question

First Name
School Subject
Your Answer

Similar Questions

  1. Substitution Method-Plz help

    Use the Substitution method to solve the system of equations. x + y = -4 x - y = 2 solve for x in the second equation. x= y+2 Put that in for x in the first equation: x+y=-4 (y+2) + y = -4 solve for y. Then, x= y+2 i don't get it.How …
  2. algebra 1

    Got a test tomorrow... Say you have a system of equations (linear), that you can solve using substitution, graphing, or elimination. Without solving the equations, can you tell if there is one solution, many solutions, or no solution?
  3. Algebra II- please help!

    I just cannot seem to be able to grasp the concept of solving polynomial inequalities. Can someone please explain, step by step, how to solve them?
  4. math

    solve each system of equations by substitution. y=3x-9 please help explain how to solve this using substitution.
  5. English

    Hi! Can somebody help me? I'm an austrian student, and i have a big problem! We have to write a definition essay with the title : tourism/ travel. and we have to write it until tomorrow, but i'm very busy, i have a mathe test tomorrow
  6. Linear Equations

    Can you please help solve this equation using the substitution method?
  7. introductory algebra

    I had these problems on my test and for some reason got them wrong. Here are the problems: Solve: x-y=9 x+y=1 The test states that the answer is (5,-4) I've checked ,y work and used substitution to solve this and still get x=4, y=-5. …
  8. substitution method

    Solve by substitution method please help me solve this. I do not know how to do this at all. The question is 3x+8y=33 and x=31-6y I know that I have to plug x into the first x like 3(31-6y)+ 8y = 33 but i do not know what to do from …
  9. Please help for my test CALculus

    using the chain rule find the min and max points and their values of the composite function defined by z=x^2+y^2, x=sin(2t), y=cos(t) This is what Ive got so far... dz/dt= 2x*dx/dt+2y*dy/dt =4sin2tcos2t-2sintcost I understand the steps …
  10. Physics

    Please help!!! Physics test!? I have a physics test tomorrow on projectile motion, and I don't feel ready for it. I'm having trouble in the class and I need to ace this test. The problem is I get confused when I get a problem. I don't

More Similar Questions