In △ ABC, a = 80, B = 100, a = 30 °, then the number of solutions of B is () A. 0b. 1C. 2D. Not sure

In △ ABC, a = 80, B = 100, a = 30 °, then the number of solutions of B is () A. 0b. 1C. 2D. Not sure

Because a = 80, B = 100, a = 30 °, according to the sine theorem: Asina = bsinb, substitute SINB = 58, because B ∈ (0, π), so B = arcsin58 or B = π - arcsin58, so choose C

80% of a number is 5 less than 35% of 45. What's the number?

(45 × 35-5) △ 80%, = (27-5) △ 80%, = 22 △ 80%, = 27.5, a: this number is 27.5

For rational numbers x and y, we define a new operation *: X * y = ax + by + C, where ABC is a constant, and the right side of the equation is the usual addition and multiplication operations,
It is known that 3 * 5 = 15,4 * 7 = 28,1 * 1 =?

Because xy = ax + by + C
And 3 * 5 = 15, 4 * 7 = 28
That is, 3 * 5 = a * 3 + b * 5 + C.1
Formula 4 * 7 = a * 4 + b * 7 + C.2
To sum up: formula 2-1 = 28-15 = (a * 4 + b * 7 + C) - (a * 3 + b * 5 + C)
That is: a = 13-2b
2 Formula * 3-1 formula * 4 = 3 * 28-4 * 15 = 3 (a * 4 + b * 7 + C) - 4 (a * 3 + b * 5 + C)
That is: B = 24 + C
1*1=a*1+b*1+c
=13-2b+24+c+c
=13-2(24+c)+24+c+c
=-11

How much is 6 meters minus 40 decimeters

One meter is 10 decimeters, so 40 decimeters is 4 meters. So 6 meters minus 40 decimeters is 2 meters

Circumference of triangle ABC
In triangle ABC, De is the vertical bisector of AC, AE = 3cm, and the perimeter of triangle abd is 13cm

∵ de vertical bisection AC ∵ Da = DC, AE = CE = 3cm
The circumference of abd = AB + AD + BD = AB + BD + DC = 13cm, AC = 6cm
The perimeter of ABC is ab + BD + CD + AC = 19cm

Shampoo 15 yuan per bottle, shopping malls to carry out promotional activities, buy 4 bottles get 1 free. Buy 4 bottles at a time, how much cheaper per bottle?

15-15 × 4 ^ (4 + 1) = 15-15 × 4 ^ 5 = 15-60 ^ 5 = 15-12 = 3 (yuan) a: it's 3 yuan cheaper per bottle

Find the maximum value of the function f (x, y) = e ^ - XY in the closed domain {(x, y) │ x ^ 2 + 4Y ^ 2 ≤ 1}

The partial derivative of F to x = - y · e ^ - XY
The partial derivative of F to y = - x · e ^ - XY
Let these two partial derivatives be equal to zero, and we get the following result
x=y=0.
That is to say, the maximum value f (0,0) = 1 is obtained at the point (0,0)

Students of two grades go on spring outings, and each grade has three classes. Mr. Xu bought 3 yuan / bottle of drinks for each student, 189 yuan, 97 yuan and 128 yuan,
Which one is right? Why?

189 yuan is right, because only 189 can be divided by three

If a, B and C are three sides of △ ABC, the result of simplifying | a-b-c | + | b-c-a | + | C-A-B |, is ()
A. -a-b-cB. a+b+cC. a+b-cD. a-b+c

∵ a, B, C are the three sides of △ ABC, ∵ a < B + C, B < C + A, C < A + B, ∵ a-b-c < 0, b-c-a < 0, C-A-B < 0, ∵ a-b-c | + | b-c-a | + | C-A-B | = B + C-A + C + A-B + A + B-C = a + B + C

On the map with a scale of 1:6000000, the distance between the two places is 5cm. The two cars run from each other at the same time, and they meet three hours later. It is known that the speed ratio of the two cars is 2:3. How many kilometers is the speed of the two cars?

5 △ 16000000 = 30000000 (CM) = 300 (km), 300 △ 3 = 100 (km), 100 × 22 + 3 = 40 (km), 100-40 = 60 (km); a: the speed of car a is 40 km / h, and that of car B is 60 km / h