What is trigonometric function?

What is trigonometric function?

Trigonometric function is a kind of transcendental function in elementary function in mathematics. Their essence is the mapping between the set of any angle and the variable of a ratio set. Generally, trigonometric function is defined in the plane rectangular coordinate system. Its domain of definition is the whole real number domain. Another definition is in the right triangle, Modern mathematics describes them as the limit of infinite sequence and the solution of differential equation, and extends their definition to complex number system
Trigonometric function will be learned in mathematics 9 of Beijing Normal University Edition
Trigonometric functions are mainly used in junior high school
Sine: sin
Cosine: cos
Tangent: Tan
Cotangent: cot
Trigonometric function of special angle
sin cos tan cot
30° 1/2 √3/2 √3/3 √3
45° √2/2 √2/2 1 1
60° √3/2 1/2 √3 √3/3
Important theorem
Sine theorem
Sine theorem: in △ ABC, a / sin a = B / sin B = C / sin C = 2R
Where R is the radius of the circumscribed circle of △ ABC
Cosine theorem
Cosine theorem: in △ ABC, B ^ 2 = a ^ 2 + C ^ 2 - 2Ac · cos θ
Where θ is the angle between edge a and edge C
Trigonometric function is very simple, as long as you can master more applications
Verification: tan20tan40tan80 is equal to tan60
Tan20tan40tan80 = tan20tan (60-20) Tan (60 + 20) = tan20 [(radical 3-tan20) / (1 + radical 3tan20)] [(radical 3 + tan20) / (1-radical 3tan20)] = tan20 [3 - (tan20) ^ 2] / [1-3 (tan20) ^ 2] = (sin20 / cos20) [3 (cos20) ^ 2 - (sin20) ^ 2] / [(cos20) ^ 2-3 (sin20)
Find the value of tan60 ` cot45 ` tan46 '
Note: tan60 'means tan60 degree, and "'" means "degree"
The first one uses the formula of double angle
Tan60 = Tan (30 * 2) = (2sin30cos30) / (cos30 * cos30-sin30 * sin30) = root 3
The second way uses the half angle formula: cot45 = 1 / tan45 = 1 / (sin90 / (1 + cos90))
tan46???
Let a be an integer, and find a so that the following equation holds
A
As long as a > 1 / 2 + 1 / 3 + 1 / 4 + 1 / 5 + 1 / 6 + 1 / 7 + 1 / 8 + 1 / 9 + 1 / 10
At the same time, a > 1.9289682539683
unsolvable
Because when a is an integer, a
The sum of the number of all subsets and all nonempty subsets of an element set is () a, 1 B, 2 C, 3 D, 4
I'm so anxious·····
If there are n elements in a set, then the number of subsets is 2 ^ n, which is the nth power of 2. It includes an empty set. Because an empty set is a subset of any set, a non empty subset is to remove an empty set
There is only one element in the set of your question, and there are two subsets. There is one nonempty subset. The answer is C
All subsets of an element set are empty sets and two subsets of itself
The sum of all nonempty subsets is 3
Choose C
C
A subset of a unit set is a set composed of an empty set and its own element, which consists of two subsets
One is a nonempty subset, so it adds up to three
I hope my answer can help you_ O ha! Continue to ask me if you don't understand~
Fill in different integers in (), < > and {} to make the equation hold
[1]1/3=1/( )+1/< > [2]1/( )-1/< >=1/6 [3]1/3+1/< >+1/{ }=1
[1]1/3=1/(4)+1/
[2]1/(4)-1/=1/6
[3]1/3+1/+1/{6}=1
=Do you think this is OK
1/3=1/(4 )+1/
[2]1/(4 )-1/=1/6
3]1/3+1/< 2>+1/{6 }=1
Set a = {a, B, C.N} what is the formula for the number of proper subsets in this set
2^n-1
2^n-2
Fill the eight integers 1-8 in the following brackets to make the equation true: (& nbsp;) (& nbsp;) = 9 () () = () () ()
36＝918＝2754．
If a = 1,2,3 and B = 1,3,4, then the number of subsets of a ∩ B is
analysis
A∩B=(1 3)
2 elements
So the number of subsets is 2 & # 178; = 4
The number of subsets is 2 ^ n (n is the number of elements)
One in 15 is a fraction plus a fraction
One in 15 is equal to the sum of four fractions? The four fractions are all one denominator and can not be the same. The sum of four fractions is equal to one in 15~
The denominators can't be the same... The four 60th denominators are the same. It's better to have the process of thinking··
1/15 = 1/25 + 1/80 + 1/100 + 1/240
1/25 + 1/100 = 1/20
1/80 + 1/240 = 1/60
1/20 + 1/60 = 1/15