Explanation:
The perpendicular slope is the negative reciprocal of the original. That means you flip the fraction to get from 10/7 to 7/10, then you flip the sign from positive to negative, going from 7/10 to -7/10.
Your math teacher or textbook may use the phrasing "flip the fraction and flip the sign" as a way to help you remember.
Note how 10/7 times -7/10 is equal to -1. This applies to any pair of perpendicular slopes as long as neither line is vertical.
