Line L passes through point (r,-s) and (t, u), is the slope of the line negative?
(1) r>t
(2) u>-s
(1) r>t
(2) u>-s
Recall that slope = (y2 - y1)/(x2-x1). So the slope is (u - (-s))/(t-r) = (u+s)/(t-r).
(1) r > t. Subtract r from both sides and get 0 > t - r . This tells us that the denominator is negative. Numerator could be positive or negative so cannot determine the sign of the slope. INSUFFICIENT.
(2). u > -s. Add s to both sides and get u + s > 0. This tells us that the numerator is positive. The denominator could be positive or negative so we cannot determine the sign of the slope. INSUFFICIENT.
(1)+(2). (1) tells us that the denominator is negative and (2) tells us that the numerator is positive. So the slope is negative.
The answer is C.
