Combinatorial Enumeration. That whole class was a rollercoaster ride of mind-blowing generating functions to prove crazy things. The exam had ridiculous questions like 'count the number of cactus trees with n vertices such that etc etc etc' and you'd do three pages of terrible terrible sums and algebra. Then your final answer would be something beautiful like n/2 and you'd breath a sigh of relief and thank the math gods.
Hello,
Line 1 is passing through (-4,3), (-2,7) has a slope of (3-7)/(-4+2)=2
Line 2 is passing through (2,9), (4,1) has a slope of (9-1)/(2-4)=-4
One other way:
y=9-1/2 x²
y'=-x
gradient 1=-(-2)=2 for point (-2,7)
gradient 2=-(4)=-4 for point(4,1)
