The object is subjected to three forces, two of which are 5N and 7n respectively. The maximum value of the resultant force of these three forces is 21n, then the size of the third force is 5N______ N. The minimum of the resultant of the three forces______ N．

The object is subjected to three forces, two of which are 5N and 7n respectively. The maximum value of the resultant force of these three forces is 21n, then the size of the third force is 5N______ N. The minimum of the resultant of the three forces______ N．

The maximum resultant force of the three forces is the sum of the three forces. Among the three forces, if the magnitude of the two forces is known to be 5N and 7n respectively, the magnitude of the third force is 21n-5n-7n = 9N; because the resultant force range of 5N and 7n is 2n-12n, the third force 9N is in the resultant force range, so the minimum resultant force is 0n, that is, if the direction of the force of 5N and 7n is opposite to that of the third force 9N, then the resultant force is 0 It is: 9, 0

In X of 5 (natural number), when x (), the fraction is true; when x (), the fraction is false; when x (), it can be changed
It's written with a fraction of three and a fifth; when x () is, the fraction is zero

When x = 1,2,3,4, the fraction is true;
When x ≥ 5, this fraction is false;
When x = 16, it can be rewritten as 3 and 1 / 5 with fraction;
When x = 0, the score is 0

If 7 / 15 + 5 is the simplest fraction with 15 as the denominator, then x may represent () natural numbers
①5 ②4 ③3 ④2

If 7 / 15 + X is the simplest fraction with 15 as the denominator, then x may represent () natural numbers
We should choose ①
Because when x = 0, 7 + X / 15 = 7 / 15
When x = 1, 7 + X / 15 = 8 / 15
When x = 4, 7 + X / 15 = 11 / 15
When x = 6, 7 + X / 15 = 13 / 15
When x = 7, 7 + X / 15 = 14 / 15
So there are five natural numbers for X