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Topic 2/3
15 Flashcards in this deck.
Solving equations using substitution involves the following steps:
Consider the system of equations:
$$ \begin{align*} y &= 2x + 3 \\ 3x + 2y &= 12 \end{align*} $$Step 1: The first equation is already solved for $y$.
Step 2: Substitute $y = 2x + 3$ into the second equation:
$$ 3x + 2(2x + 3) = 12 $$ $$ 3x + 4x + 6 = 12 $$ $$ 7x + 6 = 12 $$ $$ 7x = 6 $$ $$ x = \frac{6}{7} $$Step 3: Substitute $x = \frac{6}{7}$ back into $y = 2x + 3$:
$$ y = 2\left(\frac{6}{7}\right) + 3 = \frac{12}{7} + \frac{21}{7} = \frac{33}{7} $$>Thus, the solution is $x = \frac{6}{7}$ and $y = \frac{33}{7}$.
Substitution techniques are widely used in various mathematical and real-world applications, including:
Aspect | Substitution Technique | Elimination Technique |
Method | Isolate one variable and substitute into another equation. | Add or subtract equations to eliminate one variable. |
Ease of Use | Simple for systems where one equation is easily solvable for a variable. | Often faster for systems with coefficients that are easily combinable. |
Best For | Systems with one equation already solved for a variable. | Systems where elimination can be done without dealing with fractions. |
Advantages | Conceptually straightforward and easy to understand. | Efficient for larger systems and avoids dealing with fractions. |
Disadvantages | Can become cumbersome with complex equations or multiple variables. | May require multiplying equations to align coefficients, which can introduce complexity. |
To efficiently use substitution techniques, always double-check your isolated variable before substituting. A useful mnemonic is "I See Substitution" (I for isolate, C for check, S for substitute). For exam success, practice by solving various systems of equations to build confidence and speed. Remember to simplify equations step-by-step to avoid calculation errors.
Substitution techniques date back to ancient civilizations, where early mathematicians used similar methods to solve practical problems in trade and astronomy. Additionally, substitution isn't limited to algebra; it's a fundamental concept in computer science, particularly in programming and algorithm design, where variables are frequently replaced to optimize code efficiency.
One frequent error is incorrectly isolating a variable, leading to faulty substitutions. For example, mistakenly solving $y = 2x - 3$ as $x = 2y - 3$ instead of $x = \frac{y + 3}{2}$. Another common mistake is neglecting to substitute the entire expression, such as inserting $y = 2x + 3$ into only part of the equation $3x + 2y = 12$, resulting in an incomplete solution.