Algebra · real student question

Write the equation of the line that passes through the point (-6, 5) with slope 2/3.

Question

Write the equation of the line through the point (6,5)(-6,5) with slope m=23m=\tfrac{2}{3}.

Step-by-step solution

  1. Start from point-slope form. Given a point (x1,y1)(x_1,y_1) and a slope mm, the line is

    yy1=m(xx1)y-y_1=m\left(x-x_1\right)

    This form needs no algebra to write down — the work is entirely in simplifying it afterwards.

  2. Substitute the given values, minding the double negative. With x1=6x_1=-6, y1=5y_1=5 and m=23m=\tfrac23:

    y5=23(x(6))=23(x+6)y-5=\frac{2}{3}\left(x-(-6)\right)=\frac{2}{3}(x+6)

    Writing (x6)(x-6) instead of (x+6)(x+6) here is the most common mistake and would shift the line by eight units vertically.

  3. Distribute the slope. The fraction clears exactly because 66 is a multiple of 33:

    y5=23x+236=23x+4y-5=\frac{2}{3}x+\frac{2}{3}\cdot 6=\frac{2}{3}x+4

  4. Solve for yy to reach slope-intercept form.

    y=23x+4+5=23x+9y=\frac{2}{3}x+4+5=\frac{2}{3}x+9

    so the slope is 23\tfrac23 and the yy-intercept is (0,9)(0,9).

  5. Verify the point lies on the line. Substituting x=6x=-6:

    y=23(6)+9=4+9=5  y=\frac{2}{3}(-6)+9=-4+9=5\;\checkmark

    A second check on the slope: moving from x=6x=-6 to x=3x=-3 (a run of 33) raises yy from 55 to 77 (a rise of 22), giving 23  \tfrac{2}{3}\;\checkmark. In standard form the same line is 2x3y=272x-3y=-27.

Answer

y=23x+9y=\frac{2}{3}x+9

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