## Coordinate Geometry

In the *xy-*coordinate plane, line *m* is parallel to the *x* axis and passes through the point (4, -7). Which of the following is an equation for line *m*?

A. *x* = -4

B. *x* = -3

C. *y* = -7

D. *y* + 7 = *x* - 4

E. *y* – 7 = *x* + 4

## Knowsys Method

**Read the problem carefully. ** Take careful note that the line in the question is parallel to the *x* axis.

**Identify the bottom line.** equation for line *m* = ?

**Assess your options.** We must solve this problem by plugging the line into the point-slope formula. The point slope formula is:

**Attack the problem.** We need to use the point-slope formula, but to do so, we must determine the slope (*m*) and the y-intercept (b). It makes it a little easier to explain this problem if we draw out the line on the coordinate grid, but you do not have to do this step.

As the illustration shows, line *m* is parallel to the *x* axis, which makes it is a completely horizontal line. A horizontal line has a slope of 0. Think about it: if the *y* value never changes, then the change in *y* is zero, and no matter what the change in *x*, 0 divided by anything is 0. Since you know that the *y* value never changes, you also know the *y-*intercept will be (0,-7). Plug these values into the point-slope formula.

*y* = *mx* + *b**y* = (0)*x* -7*y* = -7

**Loop back. **Verify that you solved for the bottom line.

The correct answer is C.

This is a medium level problem.

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