1. **State the problem:** Solve the simultaneous equations for variables $x$ and $y$.
2. **General approach:** Simultaneous equations are solved by either substitution or elimination methods.
3. **Example:** Suppose the system is:
$$\begin{cases} ax + by = c \\ dx + ey = f \end{cases}$$
4. **Substitution method:** Solve one equation for one variable, then substitute into the other.
5. **Elimination method:** Multiply equations to align coefficients, then add or subtract to eliminate one variable.
6. **Intermediate step example:** If eliminating $y$, multiply first equation by $e$ and second by $b$:
$$\begin{cases} e(ax + by) = ec \\ b(dx + ey) = bf \end{cases}$$
which is
$$\begin{cases} eax + eby = ec \\ bdx + bey = bf \end{cases}$$
7. **Subtract equations to eliminate $y$:**
$$eax + \cancel{eby} - bdx - \cancel{bey} = ec - bf$$
8. **Simplify:**
$$ (ea - bd)x = ec - bf $$
9. **Solve for $x$:**
$$ x = \frac{ec - bf}{ea - bd} $$
10. **Substitute $x$ back into one original equation to find $y$:**
$$ ax + by = c \Rightarrow by = c - ax \Rightarrow y = \frac{c - a x}{b} $$
11. **Summary:** Use substitution or elimination to find $x$ and $y$ by isolating variables and simplifying.
This method works for any linear simultaneous equations with two variables.
Simultaneous Equations 45911B
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