Question

If a line has slope​ a, what is the slope of its reflection across the line y​=x?

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Part 1
The slope of its reflection across the line y=x will be

Answer 1

Check the picture below.

notice the reflected gray line on the red one over the y=x line, the slope of either line across the y=x line is simply the other's upside-down.

`\stackrel{\textit{slope of line`