什么是概率,这三件可以形成一个三角形?
随机将线段分成三个部分.多少的概率,这三件可以形成一个三角形?
设线段（0,a)任意折成三段长分别为x,y,a-x-y,显然有x>0,y>0,a-x-y>0,满足这三个约束条件的(x,y)在平面直角坐标系中的可行域为一个直角三角形,其面积为:(1/2)a^2.
三段长能构成三角形的条件是：任意两边之和大于第三边,也就是：
x+y>a-x-y,a-x-y+x>y,a-x-y+y>x同时成立
即 x+y>a/2,y 0,satisfy the three constraints (x,y) in the plane at right angles coordinate system of the feasible region of a right triangle,the area of:(1 / 2) a ^ 2.
Three paragraphs long to constitute a condition of the triangle:the sum of any two sides is greater than the third side,that is:
x + y> a-x-y,a-x-y + x> y,a-x-y + y> x at the same time set up
That is,x + y> a / 2,y