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Solve using elimination. \( \begin{array}{l}8 x+9 y=17 \\ -3 x-2 y=-5\end{array} \)

Ask by Allan Best. in the United States
Jan 30,2025

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Answer

\( x = 1 \) and \( y = 1 \).

Solution

To solve the system of equations using the **elimination method**, follow these steps: \[ \begin{cases} 8x + 9y = 17 \quad \text{(Equation 1)} \\ -3x - 2y = -5 \quad \text{(Equation 2)} \end{cases} \] **Step 1: Align the Equations** First, write the equations clearly: 1. \( 8x + 9y = 17 \) 2. \( -3x - 2y = -5 \) **Step 2: Make the Coefficients of One Variable Opposite** We'll eliminate \( y \) by making the coefficients of \( y \) in both equations opposites. To do this, find the Least Common Multiple (LCM) of 9 and 2, which is 18. - Multiply **Equation 1** by **2**: \[ 2 \times (8x + 9y) = 2 \times 17 \\ 16x + 18y = 34 \quad \text{(Equation 3)} \] - Multiply **Equation 2** by **9**: \[ 9 \times (-3x - 2y) = 9 \times (-5) \\ -27x - 18y = -45 \quad \text{(Equation 4)} \] **Step 3: Add the Modified Equations** Add **Equation 3** and **Equation 4** to eliminate \( y \): \[ \begin{align*} 16x + 18y &= 34 \\ -27x - 18y &= -45 \\ \hline (16x - 27x) + (18y - 18y) &= 34 - 45 \\ -11x &= -11 \\ \end{align*} \] **Step 4: Solve for \( x \)** \[ -11x = -11 \\ x = \frac{-11}{-11} \\ x = 1 \] **Step 5: Substitute \( x \) into One of the Original Equations** Using **Equation 1**: \[ 8x + 9y = 17 \\ 8(1) + 9y = 17 \\ 8 + 9y = 17 \\ 9y = 17 - 8 \\ 9y = 9 \\ y = \frac{9}{9} \\ y = 1 \] **Solution:** \[ x = 1 \\ y = 1 \]

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Bonus Knowledge

To use the elimination method, we want to eliminate one of the variables by making the coefficients of that variable the same in both equations. Let's focus on eliminating \( y \). First, we can manipulate the coefficients of \( y \) in both equations. Multiply the first equation by 2 and the second equation by 9: 1) \( 2(8x + 9y) = 2(17) \) → \( 16x + 18y = 34 \) 2) \( 9(-3x - 2y) = 9(-5) \) → \( -27x - 18y = -45 \) Now we can add these two equations together: \[ (16x + 18y) + (-27x - 18y) = 34 - 45 \] This simplifies to: \[ -11x = -11 \] Dividing both sides by -11 gives us: \[ x = 1 \] Now that we have \( x \), we can substitute it back into one of the original equations to find \( y \). Let's use the first equation: \[ 8(1) + 9y = 17 \] This simplifies to: \[ 8 + 9y = 17 \] Subtract 8 from both sides: \[ 9y = 9 \] Dividing both sides by 9 gives us: \[ y = 1 \] Thus, the solution to the system of equations is: \[ (x, y) = (1, 1) \]

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