Step-by-step explanation:
We will use pythagoras' Theorem for this question

where c is the longest side (in this case, the diagonal)
a and b are the 2nd and 3rd longest side (interchangeable)
given a = 10.6, b = 16.8,

-- If two lines on a graph are parallel, then their slopes are equal.
-- If two lines on a graph are perpendicular, then their slopes are
negative reciprocals.