1.
做法一：
连接AC
AC//FG
所以S△FGA = S△FGC = b2/2
做法二：
S△FGA = ABCD + FCGE - S△ABG - S△ADF - S△EFG
= a2 + b2 - (a+b)a/2 - (a-b)a/2 - b2/2
= b2/2
2.
b2/2 = 50