The solution of equation 0.9x-4 = 5 is x = ()

The solution of equation 0.9x-4 = 5 is x = ()

0.9x-4=5,0.9x=5+4,0.9x=9.x=9÷0.9,x=10.
complete.

In the equation 5x + 2-3mx + 4m = 0, where x = 1 is the root of the equation, then M =?

Substituting x = 1 into the equation, 5 + 2-3m + 4m = 0
M＝－7

Two circles C1: x + 2aX + y + A-4 = 0 a belong to R and C2: x + y-2by-1 + B = 0 B belong to R. if there are exactly three common tangents, then the minimum value of a + B is a-6b-3c-3 radical 2D3

The equation of circle C1 is (x + a) + y = 4, the equation of circle 2 is x + (y-b) = 1 ∵ there are three common tangents between circle C1 and circle C2 ∵ the distance between two centers is equal to the sum of radius, that is, (0 + a) + (B-0) = 9, a + B = 9, and the mean value theorem has a + B ≥ 2 √ ab ≤ (a + b) / 4. The solution is ab ≤ 9 / 2 if and only if a = B, the equal sign is taken

Given the vector a = (1,2), B = (- 2, - 4), C length √ 5, if (a + b) · C = 2.5, find the angle between a and C
A, B and C in the title are all vectors, including the equation and the vector in the problem

The angle between a + B = (- 1, - 2) a + B and C is 2.5 / √ 5x √ 1 + 4 = 1 / 2 = cos, the angle between a + B and C is 60 ° and the angle between a + B and a is 180 ° easily
The angle between a and C is 120 degrees

In △ ABC, ∠ C = 90 ° and the intersection line BC of AB is at D. if ∠ bad - ∠ DAC = 22.5 °, then the degree of ∠ B is______ ．

∵ De is the vertical bisector of AB, ∵ ad = BD, ∵ B = ∵ DAB, ∵ ACB = 90 °, and ∵ B + ∵ BAC = 90 °, which can be divided into two cases: ① as shown in Figure 1, ∵ B + ∵ BAC = 90 °, bad -