It is known that: in △ ABC, the edges of angles a, B and C are a, B and C respectively, and a & # 178; + C & # 178; - B & # 178; = # 189; AC (1) Find the value of cos2b (2) If B = 2, find the maximum area of △ ABC

It is known that: in △ ABC, the edges of angles a, B and C are a, B and C respectively, and a & # 178; + C & # 178; - B & # 178; = # 189; AC (1) Find the value of cos2b (2) If B = 2, find the maximum area of △ ABC

（1）cosB=1/4
cos2B=－7/8
（2）sinB=
∵ a²+c²≥2ac,∴ac≤8/3
Δ ABC area = 1 / 2acsinb ≤ root 17 / 3

Who knows the specific size (in cm) of a 1-inch, 2-inch, 3-inch, 5-inch, 6-inch, 8-inch and 10 inch photo? The more specific, the better!

Please see the table below:

What's the size of 5-inch and 6-inch photos?
Specific length and width

What's the size of a 1-inch, 2-inch, 3-inch, 4-inch, 5-inch photo?
If you know, I hope you can tell me the size of other photos!

The following is the size comparison table of common photos: specification [inch] size (CM) 1 inch 2.5 * 3.5cm ID card big head photo 3.3 * 2.22 inch 3.5 * 5.3cm small 2 inch (passport) 4.8 * 3.3cm3r [5 inch] 8.9 × 12.74r [6 inch] 15.2 × 10.25r [7 inch] 12.7 × 17.86r [8 inch] 15.2 × 20 8R [10

As shown in the figure, it is known that ∠ 1 + 2 = 180 ° and ∠ 3 = B. try to judge the relationship between ∠ AED and ∠ C, and rationalize the conclusion

It is proved that: ∵ 1 + ∠ 4 = 180 ° (definition of adjacent complementary angle) ∵ 1 + ∠ 2 = 180 ° (known) ∵ 2 = ∠ 4 (equal complementary angle of the same angle) ∥ EF ‖ AB (equal internal stagger angle, two parallel lines) ∵ 3 = ∠ ade (two parallel lines, equal internal stagger angle) and ∵ B = ∠ 3 (known) ∵ ade = ∠ B (equivalent substitution), ∥ de ‖ BC (equal angle, two parallel lines) ∵ AED = ∠ C Two straight lines are parallel and have the same angle

A figure is reduced by 1:2 and then enlarged by 3:1. Compared with the original figure, a is larger, B is smaller, and C is the same

A
Set the distance of the original image to 1, reduce it by 1:2, and then enlarge it by 3:1, and the corresponding side length is 1 / 2 × 3 = 3 / 2. 3 / 2 is larger than the original side length 1

In AutoCAD, how can I draw a 1:5 graph when I input the actual size and draw the reduced length?
For example: to draw a straight line, I input 500mm, but only draw 100mm on the graph

You first use the actual size of the drawing, and then zoom (SC), specify the scale factor of 0.2, so that the zoom out of the figure is 1:5

The area of a rectangle with a length of 18cm and a width of 12cm is 1:3

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Do you know what to ask me

As shown in the figure, a 15cm long wooden stick is vertically or obliquely placed in a wooden box with the length, width and height of 12cm, 4cm and 3cm respectively, and the length of the stick outside the wooden box is set as
Xcm, then the value range of X is

When the stick is put into the box vertically, x = 15-3 = 12cm;
When the stick is tilted into the box, the diagonal of the box = √ (12 & # 178; + 4 & # 178; + 3 & # 178;) = 13, x = 15-13 = 2cm
So, 2 ≤ x ≤ 12

As shown in the figure, five rectangles of the same size form a large rectangle. If the perimeter of the large rectangle is 28, what is the perimeter of the small rectangle?

I'm glad to answer your question
∵ perimeter is composed of 8 strips of width and 3 strips of length
Let the width be x and the length be y
8x+3y=28
y=2x
The solution equation is: 8x + 6x = 28
14x=28
x=2
Because the perimeter of the small rectangle is 2x + 2Y = 2x + 4x = 6x = 12
A: it's a small rectangle