If the lengths of three sides of a triangle are three continuous natural numbers, and its perimeter m satisfies 10 < m < 22, then the triangle has () A. 2 b. 3 C. 4 d. 5

If the lengths of three sides of a triangle are three continuous natural numbers, and its perimeter m satisfies 10 < m < 22, then the triangle has () A. 2 b. 3 C. 4 d. 5

Let the number in the middle be x, then the first one is X-1 and the last one is x + 1. From the meaning of the question, we can get: 10 ＜ X-1 + X + X + 1 ＜ 22, the solution is: 313 ＜ x ＜ 713, ∵ x is a natural number: ∵ x = 4, 5, 6, 7

If the lengths of the three sides of a triangle are three continuous natural numbers and its perimeter m satisfies 12 ＜ m ＜ 21, then the triangle has ()

Let these three edges be a, a + 1 and a + 2, where a is a positive integer
Perimeter M = a + A + 1 + A + 2 = 3A + 3 = 3 (a + 1)
If 12 ＜ m ＜ 21 is known, there are:
12＜3(a+1)＜21
That is 4

It is known that if the center line of a waist of an isosceles triangle divides its perimeter into 6 and 9 parts, then the length of its bottom edge is______ ．

Let AB = AC = 2x, BC = y, ∵ BD be the middle line on the waist, ∵ ad = DC = x, if the length of AB + ad is 6, then 2x + x = 6, the solution is x = 2, then x + y = 9, that is 2 + y = 9, the solution is y = 7; if the length of AB + ad is 9, then 2x + x = 9, the solution is x = 3, then x + y = 6, that is 3 + y = 6, the solution is y = 3; so the bottom edge of the isosceles triangle may be 3 or 7 7，3．