数学JJ第217题解题参考

irishatom

狒狒数学上面有一题几乎一模一样的题目


    

49、一个平行四边形的边长分别为6、7，问以下那个可能是平行四边形的面积？

    

(1)21 

    

(2)42 

    

(3)84

    

 

    

【答案】（1）（2）

    

【思路】

    

面积最大时为矩形，面积是：6*7=42；面积最小时，可以想象，平行四边形的一对角无限小，随之，高也变得无限小，而底边固定，面积也趋近于无穷小。因此，范围是：0<=S<42，选（1）（2）

    

 

    

lastmin

just to clarify some doubts about whether rectangle is parallelogram,

==============================================================================
A parallelogram is a 4-sided shape where opposites sides are parallel.
A rectangle is a special case of a parallelogram. All rectangles are
parallelograms.

    

But a rectangle is a shape where opposites sides are parallel *and* all
the corners are 90 degree angles. So you can't say that all
parallelograms would be rectangles. Some parallelograms would be
rectangles, but not all.

    

Rectangles are a subset of the shapes called parallelograms. But
parallelograms are *not* a subset of the shapes called rectangles.

[此贴子已经被作者于2008-5-19 16:19:10编辑过]