If two lines have slopes m and n , respectively, are they perpendicular?
1) m*n = -1
Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
EACH statement ALONE is sufficient
Statements (1) and (2) TOGETHER are NOT sufficient
The explanation says: "Statement (2) by itself is insufficient. We only know that the lines have reciprocal slopes. For example line 10x and -10x , are mirror reflections of each other on the x axis, but not perpendicular."
However since we know they aren't reciprocals we know they aren't perpendicular, thus it is sufficient!