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It is known that a, B and C are three sides of a triangle. Note: (A & sup2; + B & sup2; - C & sup2;) & sup2; - 4A & sup2; B & sup
It is known that a, B and C are the three sides of a triangle, and a & sup2; - B & sup2; - C & sup2; - 2BC is proved
It is proved that: ∵ a, B and C are the three side lengths of triangle ∵ a > 0, b > 0, C > 0, B + C > a ∵ A & sup2; - B & sup2; - C & sup2; - 2BC = A & sup2; - (B + C) & sup2; = (a-b-c) (a + B + C) respectively
If the hypotenuse of an isosceles right triangle is 2cm long, its area is_____ cm?
What's the formula? What's the difference between isosceles right triangles,
This can be done with trigonometric functions
The sine of 45 degrees is the root of two
Because the length of the hypotenuse is 2, the right angle side is root 2,
The area is the square of the root 2, multiplied by half, and that's 1
Or Pythagorean theorem, because isosceles triangle
Let the right edge be x, then 2x & sup2; = 2 & sup2; = 4
x=2,S=2×1/2=1
When the image of quadratic function y = f (x) is known, the opening upward parabola, f (- 5), f (- 1), f (4) and f (7) have four kinds of values, and only one value is not greater than zero. Draw a sketch to analyze the position characteristics of such parabola, and write an analytic formula of the function satisfying the known conditions. Can you write other analytic formulas?
It's too easy
Let f (x) = a (X-B) (x-C) a > 0
There are four kinds of function values, and only one value is not greater than zero
B and C are the points where the parabola passes on the number axis
So f (x) = a (x + 5) (x-C) C > 7
Or F (x) = a (X-7) (x-C) C
What is the difference between yjy22 and yjy23 in application?
The difference between yjy22 and yjy23 is in the outermost layer, one is polyethylene sheath and the other is PVC sheath. What are their respective applicable environments and why?
What I want to ask is the difference between 22 and 23, not 22 and 32! Learn together
Yjy22: XLPE insulated double steel strip armored PVC sheathed power cable. Applied in indoor, tunnel and directly buried soil, the cable can withstand pressure and other external forces. Yjy23: XLPE insulated double steel strip armored polyolefin sheath
Is there a YJV -- 2 (3 * 240) + 1 * 240 + 1 * 120 representation for cable representation?
Yes, 2 (3 * 240) is a double combination of three 240 phase lines. Adding 1 * 240 is a 240 as the zero line, and adding 1 * 120 is a 120 two-color line as the ground line
What is the meaning of yjv-4 * 150 + 1 * 70ct
XLPE insulated PVC sheathed cables are laid along the cable tray (CT) with four 150 square mm XLPE insulated PVC sheathed cables and one 70 square mm PE line. This is an AC three-phase five wire distribution line of TN-S system
How many megohm is the insulation resistance of the lighting circuit in the general building?
Insulation resistance test
1. Requirements: after the installation of electrical lines, the insulation resistance of all electrical lines (including exposed and concealed laying, cables) shall be tested before power transmission. If the insulation requirements are not met, power transmission is strictly prohibited
2. Purpose: to check and master the construction quality of line laying and electrical installation through insulation resistance test, so as to avoid electric leakage, short circuit and other electrical safety accidents
3
(1) Insulation test shall be conducted for exposed wiring, concealed wiring and low voltage cable in electrical wiring
(2) The 500V megohmmeter (megger) shall be used for testing, and the testing tools shall be equipped with metrological testing (model, code)
No. and period of validity
(3) The line and equipment below 48V shall be the same as the single-phase 220V line
(4) The number of tests must be in accordance with the number of circuits in the design drawing, that is, each power circuit should be tested
(5) During line test, the insulation resistance between conductors and ground shall be greater than 0.5m Ω
(6) The insulation test value of motor shall be ≥ 1m Ω
(7) The insulation test value of large electrical equipment, switch, power and lighting distribution box shall be greater than 0.5m Ω
(8) Fill in the insulation resistance test sheet carefully and ask the relevant department or the owner for acceptance
About the problem of insulation resistance test value?
Hello, everyone. I just graduated from school and learned to do data. There are many things I don't understand about the electrical installation data. How to fill in the value in the insulation resistance test record? How much is the reasonable value?
How many places are there to fill in?
Phase A-B B-C C-A
Relative zero a-N B-N C-N
Phase A-E B-E C-E
Zero to ground n
Thank you very much! I'll give 20 points first, so that I can add more points. Thank you
The insulation resistance test depends on the voltage level of the equipment you measure. Generally, the larger the insulation resistance is, the better. The equipment with low voltage of 400V is generally not less than 0.5Mb, and the equipment with 6000V is not less than 6MB, but the larger the insulation resistance is, the better the insulation of the equipment is
What does electrical zr-yjv-0.6/1kv-4 * 120 + 1 * 70sr mean
ZB refers to class B flame retardant
Yjv-0.6/1kv PVC insulated power cable, voltage class 600 ~ 1000V
Five cores, including 4 pieces of 120 square meters and 1 piece of 70 square meters
RELATED INFORMATIONS
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