Use 0123456789 to form a four digit number without repetition. If the absolute value of the difference between a thousand digit number and a single digit number is 2, how many such four digits are there

Use 0123456789 to form a four digit number without repetition. If the absolute value of the difference between a thousand digit number and a single digit number is 2, how many such four digits are there

840. (14 + 1) x (8x7)

In the space Cartesian coordinate system o-xyz, the distance between the point P (2, - 3,4) and the x-axis

The distance from P (2, - 3,4) to x-axis is the distance from P (2, - 3,4) to Q (2,0,0)
|PQ|=√(3²+4²)=5

As shown in the figure, the graph l of the linear function y = KX + B intersects the coordinate axis at points e, F and the hyperbola y = - 4 / X (x)

Because point P is on hyperbola, substituting n = - 4 / (- 1) = 4, that is, point P coordinate is (- 1.4) and y = KX + B intersects with coordinate axis at points E and f respectively, and F is the midpoint of PE, then point e coordinate is (1,0), point F coordinate is (0,2). Substituting point E and f into straight line y = KX + B, we get: k = - 2, B = 2, straight line x = A and straight line x = a

If x ∈ R, then x is an integer, X is a positive number, and X is a negative number

X ∈ Z integers x ∈ r real numbers x ∈ R + positive numbers x ∈ R - the common symbol of the set of negative numbers: n: the set of non negative integers or the set of natural numbers {0,1,2,3 }N * or N +: set of positive integers {1,2,3 }Z: Set of integers { ,-1,0,1,…… }P: Prime set Q: rational set Q +: positive rational set Q -

Known 0

loga b=1/logb a
0

Given that f (x) is a quadratic function and f (2) = - 3, f (- 2) = 7, f (0) = - 3, find the analytic expression of F (x)

Set
f(x)=ax^2+bx+c
The equation is as follows
4a+2b+c=-3
4a-2b+c=7
c=-3;
Solution
a=5/4,b=-5/2,c=-3
So f (x) = 5 / 4 x ^ 2-5 / 2 x-3

What's a * x =? (omitting the multiplier sign)

a×x=ax

Given that a and B belong to R, and 2 + AI and B + 3I are the two roots of a quadratic equation with real coefficients, then the values of a and B are?

Let the equation be X & sup2; + MX + n = 0
m. N is a real number
By Weida theorem
2 + AI + B + 3I = - M is a real number
So the imaginary part a + 3 = 0
a=-3
(2-3i) (B + 3I) = n is a real number
So the imaginary part 6-3b = 0
b=2

The formula of one variable linear regression equation and how to find ab

I suggest you go first http://baike.baidu.com/view/954762.htm Let's take a look at this place. There are two formulas for the calculation of B, and the results are the same

How to find the maximum area of an ellipse inscribed rectangle?

Let the elliptic equation be x ^ 2 / A ^ 2 + y ^ 2 / b ^ 2 = 1 (a > 0, b > 0), then (BX) ^ 2 + (Ay) ^ 2 = (AB) ^ 2
Let the vertex of the rectangle in the first quadrant be p (x, y)
So s = 4xy
S = (2 / AB) [2 (BX) (Ay)] ≤ (2 / AB) [(BX) ^ 2 + (Ay) ^ 2] = 2Ab
Take the equal sign if and only if y / x = B / A
So s max = 2Ab