1556  Calculating Area
Time Limit : 1 Second
Memory Limit : 128 MB
Submission: 186
Solved: 55
 Description
 This problem is very straightforward, in a 2D plane, Give you a polygen, you need calculate its area.
 Input
 One integer T indicates the number of test cases
Each case is started with one integer n which means the number of points of that polygen then n lines followed, each line is a pair of real number x y describe the xcoordinate and ycoordinate of point, points are descriped counter clockwise.
 Output
 One real number rounded up to 2 decimal indicates the area of polygen.
 sample input

2 4 0 0 1 0 1 1 0 1 3 0 0 1 0 1 1
 sample output

1.00 0.50
 hint
 source
 The 6th ACM Programming Contest of HUST