The following statement about prime numbers is correct: A, prime numbers have only factor 1b, all prime numbers are odd numbers C, 1 is the smallest prime number d, and prime numbers have only two factors

The following statement about prime numbers is correct: A, prime numbers have only factor 1b, all prime numbers are odd numbers C, 1 is the smallest prime number d, and prime numbers have only two factors

D. Prime numbers have only two factors

Prime number: 21 = () + () + ()

21=（ 2）+（ 2）＋（ 17）

The sum of prime numbers () and () is 21

(2) The sum of (19) and (19) is 21

In the triangular pyramid p-abc, PC vertical plane ABC, ab = BC = CA = PC, find the cosine value of dihedral angle b-ap-c

Through B as BD, vertical AC, through D as De, vertical PA to e, connect be,

Let the vectors E1 and E2 be two mutually perpendicular unit vectors. The vectors corresponding to the two sides of a right triangle are ab = 2E1 + E2 and AC = 3E1 + Ke2 respectively,
If K belongs to R, then the value of K is
There are two answers

In this question, if the right angle △ ABC, ∠ BAC is a right angle, you can do it. If not, you can't do it
From the Title Meaning: | E1 | = 1, | E2 | = 1, E1 · E2 = 0
If the vector AB is perpendicular to AC, that is, ab · AC = 0, then: (2E1 + E2) · (3E1 + Ke2) = 6 | E1 | ^ 2 + K | E2 | ^ 2 + (3 + 2K) e1 · E2
=6 + k = 0, that is, k = - 6

In the right triangle ABC, angle B = 90 degrees, AC = 200. Sina = 0.6, find the length of BC
(A) BC = 110 (b) BC = 1200 (c) BC = 100 (d) BC = 120 hint: Sina=

d

1 / 2 (the square of a + the - 2nd power of a) = 41 / 9
How to reduce to the fourth power of 9A - the square of 82a + 9 = 0

1 / 2 (A & # 178; + A ^ - 2) = 41 / 9 ｛ 1 / 2 (A & # 178; + 1 / A & # 178;) = 41 / 9 ｛ (a ^ 4 + 1) / 2A & ｛ 178; = 41 / 9 ｛ 82a & ｛ 178; = 9 (a ^ 4 + 1) ｛ 9A ^ 4-82a & ｛ 178; + 9 = 0. If you are satisfied, please click [satisfactory answer]; if you are not satisfied, please point out, I will correct it! I hope to return you

As shown in the figure, + circle O is the circumscribed circle of triangle ABC, + BD is the tangent of circle O, + is ∠ CBA and ∠ CBD equal? + why is it urgent

You don't have the picture above
But I can tell you, it's not necessarily equal. And it's not equal in most cases

If u = {1,2,3,4,5}, M = {1,2,4}, n = {3,4,5}, then ∁ U (m ∩ n) = ()
A. {1，2，3，5}B. {1，2，3}C. {1，3，4}D. {4}

∵ set M = {1,2,4}, n = {3,4,5}, ∩ m ∩ n = {4}, ∩ complete set u = {1,2,3,4,5}, ∁ U (m ∩ n) = {1,2,3,5}

As shown in the figure, in △ ABC, D is a point on the BC extension line, and the angular bisectors of ∠ ABC and ∠ ACD intersect at point E

It is proved that: be is the bisector of ABC, EBC = 12 ABC, CE is the bisector of ACD, ACE = 12 ACD = 12 (∠ a + ∠ ABC), ABC + ACB = 180 ° i.e. ∠ ABC + ACB = 180 ° - a 1, e + EBC + ACB + ace = 180 ° i.e. ∠ e + 12 ABC + ACB + 1