Question regarding FF 7th edition Question #13

simkeechai

the question was listed in chinese, below is my translation:



Q. Knowing that this line segment passes thru point a (r, -s) and point
b (t, u). Ask, what is the slope of this line, positive or negative?

1) r > t;

2) u > -s



the answer from FF is: C



here's my understanding on this question. since the y co-ordinate of
point a is negative, and y co-ordinate of point b is positive, we can
infer that point b lies on the upper portion of the x-y co-ordinate
system and point a lies on lower portion of the x-y co-ordination
system.



with the information from 1, we know that r is greater than t, which
means r is on the right hand side and t is on the left hand side of the
x-y co-ordinate system.



combine the question with the information from 1, we know that point b
lies on the upper left of the co-ordinate and point a lies on the
bottom right of the co-ordinate. so, i guess the line is downward
sloping, which is negative. am i right?



here's my another concern about this question. do i need to assume the
positive or negative values of each of r, s, t, and u? since the
relative values for points a and b already stated in the question.



please correct me if i were wrong.

horsefish

斜率K=(y2-y1)/(x2-x1)=(-u-s)/(r-t) 再根据条件1,2 带入, 可得C