Set a = {a, B, C.N} what is the formula for the number of proper subsets in this set? Why is 2 ^ n-2

Set a = {a, B, C.N} what is the formula for the number of proper subsets in this set? Why is 2 ^ n-2

The one above is basically right, but it's 2 ^ n-1, because an empty set is a proper subset of any set
Which formula is used to calculate the number of subsets of set a = 0,1,2,3,4?
There are five elements, so the number of subsets is 2 ^ 5 = 32
Definition and properties of inverse proportion function
Generally, if the relationship between two variables X and y can be expressed as y = K / X (k is a constant, K ≠ 0), then y is said to be the inverse proportional function of X. because y = K / X is a fraction, the value range of independent variable x is x ≠ 0. Sometimes y = K / X is also written as xy = K
It is known that F1 and F2 are the two focal points of the ellipse x216 + Y29 = 1. The straight line passing through point F2 intersects the ellipse at two points a and B. in △ af1b, if the sum of two sides is 10, then the length of the third side is______ .
∵ A and B are on the ellipse x216 + Y29 = 1, ∵ AF1 | + | af2 | = 8, | BF1 | + | BF2 | = 8 ∵ AF1 | + | af2 | + | BF1 | + | BF2 | = 16 ∵ AF1 | + | BF1 | + | ab | = 16 ∵ in △ af1b, the sum of two sides is 10, and the length of the third side is 16-10 = 6, so the answer is 6
Let a = 1.1 ^ 0.9, B = 0.9 ^ 1.1, C = log, with 1.1 as the base and 0.9 as the logarithm, then the relationship between ABC and its size is established
Combined with logarithmic function and exponential function images, it is easy to know that log is based on 1.1 and 0.9 〈 0,
0 〈 0.9 ^ 1.1 〈 1,1.1 ^ 0.9 〉 1, so we get C
a> Just draw the picture below
Inverse scale function positive scale function
A function in the form of y = K / X (K ∈ R and K ≠ 0) is called an inverse proportional function. The domain of definition of the inverse proportional function is {x | x ≠ 0}, and the range of values is (- ∞, 0) ∪ (0, + ∞)
A function of the form y = KX (k is a constant and K ≠ 0) is called a positive proportion function. The domain of definition and range of value of a positive proportion function are R (real number set)
Learn to be strong, to be a right person, it is strong for you!
It is known that f1.f2 is the two focal points of the ellipse X & # 178 / 9 + Y & # 178 / 16 = 1. If | AB = 5 |, then | AF1 | + | BF1 | is equal to?
AF1＋AF2=2a,BF1＋BF2=2a
By adding the two formulas, we can get the following result:
AF1＋AF2＋BF1＋BF2=4a
(AF2＋BF2)＋(AF1＋BF1)=4a
AB＋[AF1＋BF1)=4a
AF1＋BF1=4a－AB=16－5=11
How to compare the logarithm of base 8 with that of base 9?
Construct a function LG (x + 1) / lgx
We can get [xlgx - (x + 1) LG (x + 1)] / s by solving its derivative
S is the denominator in the process of solving, because it is easy to see that this series of formulas (s) must be greater than 0, so it is directly expressed as s without affecting the calculation
We can see X
Using the formula of changing bottom
Log7 (base) 8 (true) = LG8 / lg7
Lg9 / log8
[lg7(8))]/[lg8(9)]
=[lg8/lg7]/[lg9/lg8]
= [lg8]^2/[lg7*lg9]
>1
So we can launch LG8 / lg7 > lg9 / LG8
So log7 (base) 8 (true) > log8 (base) 9 (true)
Positive scale function inverse scale function
Positive scale function y = KX + B and inverse scale function y = K / X
If you ask this question, are the k values of the two formulas the same?
If it's different, he should say y = K1X + B and y = K2 / X
Is that right?
Well, it should be. If the problem is very strict and regular, the value of K is the same
no
It is known that a straight line passes through the right focus F2 of the ellipse quarter X & # 178; + Y & # 178; = 1, and intersects the ellipse at two points a and B. point F1 is elliptic
The perimeter of △ af1b is measured in the left focus
∵ the line AB passes through the right focus F2 of the ellipse, ∵ af2 + BF2 = ab
According to the definition of ellipse, there are: AF1 + af2 = 2A = 2 × 2 = 4, BF1 + BF2 = 2A = 4
∴AB＋AF1＋BF1＝AF2＋BF2＋AF1＋BF1＝（AF1＋AF2）＋（BF1＋BF2）＝4＋4＝8.
The perimeter of ∧ af1b is 8