摘要
已知平行四边形两邻边a、b(a≤b)及对角线夹角α(0°<α<90°)求其面积是一类常见习题。教师在编制这类例题时应注意判断条件tgα/2≤α/b的成立,否则会出现失误。在解答这类习题时亦应注意判断此式是否成立。
It is the type of common problems that the area of a parallelogram is computed, if two adjacent sides a, b(a≤b) and included angle a(0°<a<90°)between two diagonal lines of the parallelogram are known. The teacher must verify the condition tga/2<a/b when he works out these problems; if not, there'll mistake. It must is verified condition tga/2<a/b when these problems are solved, too.
