The coefficient of the unknowns of equation 2x = 14 is reduced to 1, and () A. x=2B. x=18C. x=12D. x=8

The coefficient of the unknowns of equation 2x = 14 is reduced to 1, and () A. x=2B. x=18C. x=12D. x=8

If the coefficient is changed to 1, x = 18, so B

Let {X / 4 = Y / 5,3x-2y = 10} solve the system of equations (let K be an unknown number)

Let X / 4 = Y / 5 = k, then x = 4K, y = 5K
Substituting 3x-2y = 10, 12k-10k = 10
The solution is k = 5
So x = 20, y = 25

Let x, y be independent of each other, and n (1,2) n (0.1), then the expectation of Z = 2x-4y + 3?

E(Z)=E(2X-4Y+3)=2E(X)-4E(Y)+E(3)
=2-0+3
=5

If a + 3b is perpendicular to 7a-5b and a-4b is perpendicular to 7a-5b, the angle between a and B is obtained

A-4b is perpendicular to 7a-5b, a + 3b is perpendicular to 7a-5b, so a + 3b and a-4b are opposite vectors, so a + 3B = - A + 4b, that is, B = 2A, so the angle between a and B in the same direction is 0 degree

BD and CE are bisectors of the outer angle of triangle ABC respectively. Through point a, they make AF vertical BD and Ag vertical CE. The perpendicular foot is f.g. they connect FG and extend AF.AG ,...
BD and CE are bisectors of the outer angle of triangle ABC respectively. Through point a, they make AF vertical BD and Ag vertical CE. The perpendicular foot is f.g. they connect FG and extend AF.AG , intersect with the straight line BC at m.n, find the description FG = 1 / 2 (AB + BC + AC)

∵ AF⊥BD ∴ ∠AFB= ∠MFB
∵ BD, bisecting ∠ ABM ∫ M = ∠ Fab ∫ AB = BM AF = MF
Similarly, AC = CN, Ag = GN
∵ AF=MF AG=GN ∴FG=1/2 MN
∴ FG=1/2(AB+BC+AC)

By using the definition of function monotonicity, it is proved that the function f (x) = 3x-1 is a monotone increasing function on (negative infinity, positive infinity)

By using the definition of function monotonicity, it is proved that the function f (x) = 3x-1 is a monotone increasing function on (negative infinity, positive infinity)
It is proved that f (x) = 3x-1
Take X1 at R

Some mathematical problems about vector
1. Given 8 nonzero real numbers A1. A2. A3 Proof: the following six real numbers: A1 * A3 + A2 * A4
A1 * A5 + A2 * A6. A1 * A7 + A2 * A8. A3 * A5 + A4 * A6. A3 * A7 + A4 * A8. A5 * A7 + A6 * A8
2. Prove that two numbers a and B can be taken from any four different real numbers
Make 1 + AB > (1 / 2) * SQR ((1 + A ^ 2) (1 + B ^ 2))

1. Select four vectors a (A1, A2), B (A3, A4), C (A5, A6), D (A7, a8) randomly, then the real numbers given in the question are a · B, a · C, a · D, B · C, B · D, C · D respectively. Suppose that the angle between the three vectors is greater than 90 degrees, and the angle between the vectors is always less than 180 degrees, the three vectors can be translated to a common vertex

In triangle ABC, extend BC to point D, the bisector of angle ABC and the bisector of angle ACD intersect at point E, try to prove that angle e = 1 / 2 angle A

∵∠A=180°-2∠CBE-(180°-2∠ECD)=180°-2∠CBE-180°+2∠ECD=2(∠ECD-∠CBE)=2∠E∴∠E=1/2∠A

For a job, Party A will do it alone for 20 hours, and Party B will do it alone for 12 hours. Now Party A will do it alone for 4 hours, and the rest will be done by Party A and Party B together. How many hours will it take to complete the rest?

Suppose that the remaining part needs x hours to complete, 120 × 4 + (120 + 112) x = 1, x = 6. Answer: the remaining part needs 6 hours to complete

If △ ABC is inscribed in a circle with o as the center and 1 as the radius, and the vector 3oa + 4ob + 5oC = O, then ① calculate the vector OA · ob, ob · OC, OC · OA. ② calculate the area of △ ABC
HELP!

(1) ∵ a, B, C are on the unit circle, ∵ OA = ︱ ob = ︱ OC = 1, and the negative direction of OC and X axis coincides, so OC = icos180? + jsin180? = - I, 5oC = - 5I. ∵ 3oa + 4ob = - 5oC = 5I. Therefore, we can take a point D in the positive direction of X axis to make od = 5, and use od as the bevel, 3 OA = 3, 4 ob = 4 as the right angle triangle