Question

A student writes the equation for a line that has a slope of -6 and passes through the point (2, –8).

y -(-8) = -6(x - 2)

y -(-8) = -6x + 12

y -(-8) + 8 = -6x + 12 + 8

y = -6x + 20

Explain why the work is not correct.

Answer 1

The student should have simplified the equation to have y + 8 on the left.

Then, the student should have subtracted 8 from both sides of the equation.

The value of b should be 4, not 20.

Explanation:

Answer 2

The error in the students work is

y -(-8) + 8 = -6x + 12 + 8

subtracting a negative is adding

y+8

They should subtract 8 from each side instead of adding 8 to each side

Explanation:

We can use point slope form since we are given a point and the slope

y-y1 = m( x-x1)

y--8 = -6(x-2)

y+8 = -6(x-2)

Distribute the -6

y+8 = -6x+12

Subtract 8 from each side

y+8-8 = -6x+12-8

y = -6x+4

The error in the students work is

y -(-8) + 8 = -6x + 12 + 8

subtracting a negative is adding

y+8

They should subtract 8 from each side instead of adding 8 to each side