posted by Lisa on .
Determine whether the lines are parallel, perpendicular, or neither.
y = 9x + 9 and y = -9x + 9
Is this perpendicular since they go across from each other
The answer is neither. For the lines to be perpendicular, the product of the slopes, which are coefficients of the "x" terms, must be -1. In this case the product is -81.