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Solve the simultaneous equations. Show all your work.

[tex]\[
\begin{array}{r}
3x + y = 11 \\
x^2 - 2y = 18
\end{array}
\][/tex]


Sagot :

Alright, let's solve the system of equations step by step.

We are given:

[tex]\[ 3x + y = 11 \quad \text{(Equation 1)} \][/tex]
[tex]\[ x^2 - 2y = 18 \quad \text{(Equation 2)} \][/tex]

### Step 1: Express [tex]\( y \)[/tex] in terms of [tex]\( x \)[/tex] from Equation 1

Rearrange Equation 1:

[tex]\[ y = 11 - 3x \][/tex]

### Step 2: Substitute [tex]\( y \)[/tex] into Equation 2

Replace [tex]\( y \)[/tex] in Equation 2 with [tex]\( 11 - 3x \)[/tex]:

[tex]\[ x^2 - 2(11 - 3x) = 18 \][/tex]

### Step 3: Simplify the resulting equation

Distribute the -2 inside the parentheses:

[tex]\[ x^2 - 22 + 6x = 18 \][/tex]

Move all terms to one side to form a standard quadratic equation:

[tex]\[ x^2 + 6x - 40 = 0 \][/tex]

### Step 4: Solve the quadratic equation

We can factor the quadratic equation:

[tex]\[ (x + 10)(x - 4) = 0 \][/tex]

So, the solutions for [tex]\( x \)[/tex] are:

[tex]\[ x = -10 \quad \text{or} \quad x = 4 \][/tex]

### Step 5: Solve for [tex]\( y \)[/tex] using the values of [tex]\( x \)[/tex]

Case 1: If [tex]\( x = -10 \)[/tex]

[tex]\[ y = 11 - 3(-10) \][/tex]
[tex]\[ y = 11 + 30 \][/tex]
[tex]\[ y = 41 \][/tex]

Case 2: If [tex]\( x = 4 \)[/tex]

[tex]\[ y = 11 - 3(4) \][/tex]
[tex]\[ y = 11 - 12 \][/tex]
[tex]\[ y = -1 \][/tex]

### Step 6: Write the solutions as ordered pairs [tex]\( (x, y) \)[/tex]

The solutions to the system of equations are:

[tex]\[ (-10, 41) \quad \text{and} \quad (4, -1) \][/tex]

Thus, the solutions are:

[tex]\[ \boxed{(-10, 41) \text{ and } (4, -1)} \][/tex]