There are four line segments with length of 1.2.3.4. Three of them can form a triangle

There are four line segments with length of 1.2.3.4. Three of them can form a triangle

Three out of four cases: C (4,3) = 4 kinds
As long as there is 1, it must not form a triangle, that is, only 2, 3, 4 can meet
Probability: 1 / 4

From the five line segments with length of 1,2,3,4,5, if any three of them are selected as edges, the probability of forming an obtuse triangle is______ .

From the five line segments of length 1, 2, 3, 4, 5, take any three, all cases have C
Three
Five
=10 kinds,
When the three sides can form an obtuse triangle, the cosine value of the largest side must be less than zero, that is, the sum of squares of the smaller two sides is less than the square of the third side,
Therefore, there are only 2, 3, 4 and 2, 4, 5 to form an obtuse triangle,
Therefore, the probability of forming obtuse triangle is 2
10=1
5，
So the answer is 1
5．

There are six line segments with the length of 1,2,3,4,5,6. If you take any three of them, do you have to form a triangle? What is the probability of forming a triangle?

0

For ABC, the angle of a is obtuse 3, a = 4, B = 5, then C =___ .

∵ a = 4, B = 5, △ ABC area s = 1
2absinC=5
3，
∴sinC=
Three
2，
∵ C is an obtuse angle,
∴C=120°，
According to the cosine theorem, C2 = A2 + b2-2abcosc = 16 + 25-20 = 21,
Then c=
21，
So the answer is:
Twenty-one

Given the obtuse triangle with three sides 2, 3, x, find the range of X?

One
If x is the largest side and is a right triangle,
2*2+3*3＝x^2
X = root 13, so root 13

It is known that the three sides of a triangle are: 2, 3 and 4. Is this an obtuse triangle? Why

If the length of the side opposite the largest angle is 4, let the maximum angle be a, so cosa = (2 + 3-4) / 2 × 2 × 3 = - 1 / 4, so ∠ a ＞ 90 ° is an obtuse triangle

As the title What e and D With N, P Related to expectations and standard deviations

Binomial distribution e = NP d = NP (1-p)
Geometric distribution e = P / 1 d = P2 / (1-p)

All formulas of mathematical probability in Senior High School

The classical probability model P (a) = the number of basic events contained in a / the total number of basic events. The geometric probability p (a) = a area / total area conditional probability p (a | b) = nab / Nb = P (AB) / P (b) = the number of basic events contained by AB / the number of basic events contained by B (this is difficult to type) the Bernoulli type is more difficult to find, PN (k) = CN * P ^ K

Senior high school mathematics permutation and combination probability There are three tourist groups, four scenic spots, four scenic spots can be selected at will, ask the probability that there are two scenic spots without a tour group

p=C(2,4)C(2,3)C(1,2)/C(1,4)^3
=6*3*2/4^3
=9/16

What is the formula of permutation and combination in probability operation?

0