算法错误，查找线之间的区域。

I was doing my math hw, and it required me to calculate areas between 2 lines. I solved couple of them, I got them right(its online so it shows me whether i got it wrong or right), then I thought about writing a program that does the calculation for me, I created a nice algorithm, used java for the program, but in the end it didn't give me the right answer. I put the data from one of the questions I already solved whether i got it right or wrong.I was doing my math hw, and it required me to c