Solve the System of Equations: -5x+9y=18 and x+8y=16 Using Substitution

Find the value of x and and band the substitution method.

{5x+9y=18x+8y=16 \begin{cases} -5x+9y=18 \\ x+8y=16 \end{cases}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve the system of equations
00:04 Isolate X
00:12 This is the expression for X, substitute in the second equation to find Y
00:33 Properly expand brackets, multiply by each factor
00:46 Isolate Y
00:58 Collect like terms
01:17 This is the value of Y
01:22 Now substitute the value of Y to find X
01:40 And this is the solution to the problem

Step-by-step written solution

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1

Understand the problem

Find the value of x and and band the substitution method.

{5x+9y=18x+8y=16 \begin{cases} -5x+9y=18 \\ x+8y=16 \end{cases}

2

Step-by-step solution

To solve the given system of linear equations using the substitution method, follow these steps:

  • Step 1: Solve the second equation for x x .

From the second equation:

x+8y=16 x + 8y = 16

We can solve for x x as follows:

x=168y x = 16 - 8y
  • Step 2: Substitute the expression for x x into the first equation.

Substitute x=168y x = 16 - 8y into the first equation:

5(168y)+9y=18 -5(16 - 8y) + 9y = 18

Simplify and solve for y y :

- Distribute 5-5:

80+40y+9y=18 -80 + 40y + 9y = 18

- Combine like terms:

49y80=18 49y - 80 = 18

- Add 80 to both sides:

49y=98 49y = 98

- Divide by 49:

y=9849=2 y = \frac{98}{49} = 2
  • Step 3: Substitute y=2 y = 2 back into the expression for x x .

The expression for x x is:

x=168y x = 16 - 8y

- Substitute y=2 y = 2 :

x=168(2) x = 16 - 8(2) x=1616 x = 16 - 16 x=0 x = 0

Therefore, the values that satisfy both equations in the system are x=0 x = 0 and y=2 y = 2 .

3

Final Answer

x=0,y=2 x=0,y=2

Practice Quiz

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Solve the following equations:

\( \begin{cases} 2x+y=9 \\ x=5 \end{cases} \)

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