2x - y = 5 - Parker Core Knowledge

Understanding the Context

What Is the Equation 2x – y = 5?

The equation 2x – y = 5 is a linear equation in two variables, x and y. It represents a straight line on the Cartesian coordinate plane, where changing the value of x affects the corresponding value of y in a predictable, linear way.

Rewritten in standard form, the equation looks like this:
2x – y – 5 = 0
Or equivalently:
y = 2x – 5

This slope-intercept form (y = mx + b) makes it easy to identify key features:

• Slope (m): 2 — indicates the line rises 2 units for every 1 unit increase in x
  
• Y-intercept (b): –5 — the point where the line crosses the y-axis at (0, -5)

Key Insights

How to Solve 2x – y = 5

Solving this equation involves isolating one variable in terms of the other — or finding specific values of x and y that satisfy the relationship.

Step 1: Solve for y in terms of x

As shown earlier, the equation simplifies to:
y = 2x – 5
This is useful for graphing or analyzing how y changes with x.

Step 2: Solve for x in terms of y

Rewriting the original:
2x – y = 5
→ 2x = y + 5
→ x = (y + 5)/2

Final Thoughts

Step 3: Finding Specific Solutions

To find a specific point, pick any x or y and compute the other.

Example:
If x = 3, then
y = 2(3) – 5 = 6 – 5 = 1
So the point (3, 1) lies on the line.

Graphing the Line 2x – y = 5

Plotting the equation on a coordinate plane reveals its geometry:

• Start at the known y-intercept (0, –5)
  
• Use the slope (2 = rise/run) — move up 2 units and right 1 unit to find the next point at (1, –3)
  
• Connect these points to draw the straight line extending infinitely in both directions

Graphing helps visualize how changes in x directly influence y — a core concept in algebra and calculus.