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If a matrix and its transpose are multiplied into an identity matrix, what is the matrix?
Orthogonal matrix. Of course, only refers to the square matrix
The characteristics of orthogonal matrix: the absolute value of determinant is 1, the row and column are the standard orthogonal basis of vector space with the same dimension as the order of matrix, the length and inner product are not changed as linear transformation, etc
Given the inverse matrix of the second order matrix, how to find the second order matrix
This is the same as finding a ^ - 1 from a
This is because a = (a ^ - 1) ^ - 1
A=
a b
c d
Using the formula A ^ - 1 = (1 / | a |) a*
Where: | a | = ad BC
A*=
d -b
-c a
Note memory method: the main diagonal exchange position, sub diagonal negative sign
Finding the inverse of a second order matrix
[1 2] -1 = -1/2[4 -2]
[3 4] [-3 1]
How did this - 1 / 2 come from
The inverse matrix of the second order is the adjoint matrix. The main diagonals exchange, the sub diagonals exchange and sign change
Wrong, not equal
But what's this - 1 / 2
Divide by determinant 1 2
3 4|
=4-2×3=-2
In angle ABC, ab = AC = 5, BC = 6, then what is tanb?
Let B C be the intersection of high ad on the edge of B C, and B C be the triangles of isosceles on D, so BD = CD = 3, ad = 4, so tan B = 4 / 3, Tan (A / 2) = 3 / 4, Tan a = 2tan (A / 2) / (1-tan ^ (A / 2)) = 3 / 2 / (1-9 / 16) = 24 / 7
Translate some phrases into English!
Let sb do sth_______________
Why not get some ice cream_______________________________ ?
Boxes of candy__________________
Let sb do sth make sb do sth why don't we get some ice cream? How about getting some ice cream
In △ ABC, the opposite sides of ∠ a, ∠ B and ∠ C are a, B and C respectively. If a = 60 ° and B and C are the two roots of the equation x2-7x + 11 = 0, then a is equal to______ ．
According to the meaning of the question, we can know that B + C = 7, BC = 11, B2 + C2 = (B + C) 2-2bc = 27, cosa = B2 + C2 − a22bc = 27 − a222 = 12, and get a = 4
All phrases containing in
In (a) disturbance in (full) bloom in (high) glee in (single) file in (the) large scale in (the) light of in (the) process of In the process, in a Guise with My appearance
Add the same natural number to the numerator and denominator of 1 / 13 at the same time to get another fraction equal to 1 / 2. What is the natural number?
What's the formula
（1+n）/(13+n)=1/2
The solution is n = 11
Is there any difference between noun modifying noun and adjective modifying noun?
Of course!
This is similar to the so-called parallel relation and progressive relation
When rank modifies a noun, it belongs to several equally important expression object sequences. The loss of any keyword in the sequence has the same effect on the original sentence
When you say adj + n., the key point is n. if n is gone, the change of sentence meaning is larger than that of only removing one adj~
The above is my personal understanding, thought for a long time to come to an end
Another example is apple tree. Since Apple has no adj form, there is no difference
Most of the time, N1 in N1 and N2 has the form of adj
If we use adj instead of N1, the original meaning of the sentence may be changed completely
If the function f (x) = x3-3x-k has only one zero point on R, then the value range of constant k is______ ．
If f ′ (x) = 3x2-3, Let f ′ (x) = 0, the solution is x = 1 or x = - 1. By using the sign of derivative, we can get that f (x) is an increasing function on (- ∞, - 1), a decreasing function on (- 1,1), and an increasing function on (1, + ∞)
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