Solve 3x 4y 12 For Y

Solving 3x + 4y = 12 for y: A Comprehensive Guide

This article provides a comprehensive guide on how to solve the equation 3x + 4y = 12 for y. We will explore various methods, delve into the underlying mathematical principles, and address common questions students may have. Understanding how to isolate variables in linear equations is a fundamental skill in algebra, crucial for solving more complex problems in mathematics and science. This guide will not only show you how to solve for y but also why the steps work, equipping you with a deeper understanding of algebraic manipulation.

Introduction: Understanding Linear Equations

Before diving into the solution, let's establish a foundational understanding of linear equations. A linear equation is an equation that represents a straight line on a graph. It typically involves two variables, usually denoted as x and y, and the highest power of each variable is 1. The general form of a linear equation is Ax + By = C, where A, B, and C are constants. Our equation, 3x + 4y = 12, perfectly fits this description. Solving for a specific variable means isolating that variable on one side of the equation, expressing it in terms of the other variable and constants. In this case, our goal is to isolate 'y'.

Step-by-Step Solution: Isolating y

The process of solving 3x + 4y = 12 for y involves manipulating the equation using algebraic rules to get 'y' by itself on one side of the equals sign. Here's a step-by-step breakdown:

Step 1: Subtract 3x from both sides

Our primary goal is to move all terms not involving 'y' to the right side of the equation. We achieve this by subtracting 3x from both sides of the equation. This maintains the equality because we perform the same operation on both sides.

3x + 4y - 3x = 12 - 3x

This simplifies to:

4y = 12 - 3x

Step 2: Divide both sides by 4

Now, 'y' is being multiplied by 4. To isolate 'y', we need to perform the inverse operation – division. We divide both sides of the equation by 4:

(4y) / 4 = (12 - 3x) / 4

This simplifies to:

y = (12 - 3x) / 4

Step 3: Simplify (Optional)

While the equation is now solved for y, we can further simplify the expression on the right-hand side by dividing each term within the parenthesis by 4:

y = 12/4 - (3x)/4

This simplifies to:

y = 3 - (3/4)x

Or, equivalently:

y = - (3/4)x + 3

This final form, y = -(3/4)x + 3, is the slope-intercept form of a linear equation (y = mx + b), where m is the slope (-3/4) and b is the y-intercept (3). This form is particularly useful for graphing the equation.

Graphical Representation and Interpretation

The equation 3x + 4y = 12 represents a straight line. Solving for y allows us to easily plot this line on a Cartesian coordinate system. The slope-intercept form, y = -(3/4)x + 3, directly tells us the y-intercept (the point where the line crosses the y-axis) is 3. The slope, -3/4, indicates that for every 4 units increase in x, y decreases by 3 units. This negative slope signifies a downward-sloping line.

Mathematical Explanation: Properties of Equality

The steps we took to solve for y are based on fundamental properties of equality. These properties ensure that the manipulations we perform maintain the equivalence of the equation:

• Subtraction Property of Equality: If you subtract the same quantity from both sides of an equation, the equation remains true. This is what we used in Step 1.
• Division Property of Equality: If you divide both sides of an equation by the same non-zero quantity, the equation remains true. This is what we used in Step 2.

These properties, along with the addition and multiplication properties of equality, are the cornerstones of algebraic manipulation. Understanding these properties is crucial for confidently solving any algebraic equation.

Alternative Methods: Using the Elimination Method

While the method outlined above is the most straightforward for solving this specific equation for y, let's briefly consider alternative approaches, particularly useful when dealing with systems of equations. The elimination method could be applied if you were solving a system of equations involving 3x + 4y = 12 alongside another equation. However, for isolating 'y' in this single equation, the direct method (as shown above) remains the most efficient.

Frequently Asked Questions (FAQs)

Q1: What if I made a mistake in one of the steps?

A1: It’s perfectly normal to make mistakes, especially when learning algebra. Carefully review each step, paying close attention to the signs and operations. If you are still struggling, try working through the problem again, or seek assistance from a teacher, tutor, or online resources.

Q2: Can I solve for x instead of y?

A2: Absolutely! To solve for x, follow a similar process but with different steps:

1. Subtract 4y from both sides: 3x = 12 - 4y
2. Divide both sides by 3: x = (12 - 4y) / 3
3. Simplify (optional): x = 4 - (4/3)y

Q3: What is the significance of the slope and y-intercept in the final equation?

A3: The slope (-3/4) indicates the steepness and direction of the line. A negative slope means the line slopes downwards from left to right. The y-intercept (3) represents the point where the line intersects the y-axis.

Q4: How can I check my answer?

A4: Substitute your solution for y back into the original equation (3x + 4y = 12). If the equation holds true, your solution is correct. For example, if you found y = 3 - (3/4)x, substitute this back into 3x + 4(3 - (3/4)x) = 12. Simplify the equation, and if it simplifies to a true statement (like 12 = 12), then your solution for y is correct.

Conclusion: Mastering Algebraic Manipulation

Solving the equation 3x + 4y = 12 for y is a fundamental algebraic skill. By mastering the steps outlined above, you’ve not only solved this specific equation but also developed a stronger understanding of algebraic manipulation. Remember to practice regularly, and don't hesitate to seek help when needed. The ability to isolate variables is a building block for more advanced mathematical concepts and applications across various fields. Continue practicing, and you will build confidence and proficiency in solving linear equations and tackling more complex algebraic problems. This understanding will serve as a valuable asset in your mathematical journey.