If you are asking for slope, the slope of one line is m, the slope of the other is -1/m. For example, if the slope for one line is 5, the slope of the other line is -1/5 = -0.2 . (Math Open Reference)
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If it's not 90 degrees, then they're not perpendicular.
Yes. That's one definition of "perpendicular".
Yes.
draw two intersecting lines that are not perpendicular
Yes, that is the definition of perpendicular. 2 lines intersecting to form a right(90o) angle.