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Write the equation of a line from its slope and y-intercept

A line with slope mm and yy-intercept bb is represented by y=mx+by=mx+b, where mm describes the constant rate of change and bb is the value of yy when x=0x=0, so its graph passes through (0,b)(0,b). This understanding includes positive, negative, zero, and fractional slopes and supports translating between an equation, a graph, and a verbal relationship; vertical lines, undefined slopes, and more advanced forms of line equations are not included.

Detailed Explanation: Write the equation of a line from its slope and y-intercept

A line with slope mm and yy-intercept bb can be written in slope-intercept form:

y=mx+by=mx+b

To write the equation:

  1. Identify the slope mm.
  2. Identify the yy-intercept bb.
  3. Substitute those values into (y=mx+b)(y=mx+b).
  4. Simplify if needed.

Example: Write the equation of a line with slope (−23)(-\frac{2}{3}) and yy-intercept 44.

The slope is

m=−23m=-\frac{2}{3}

and the yy-intercept is

b=4.b=4.

Substitute these values into the formula:

y=mx+by=mx+b y=−23x+4y=-\frac{2}{3}x+4

So, the equation of the line is

y=−23x+4\boxed{y=-\frac{2}{3}x+4}

The yy-intercept of 44 means the line passes through ((0,4))((0,4)). The slope (−23)(-\frac{2}{3}) means that for every 33 units moved to the right, the line moves 22 units down.

Learn by doing: Write the equation of a line from its slope and y-intercept

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Slope of a Line - Select Linear Equation Based on Graph


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