Anbn... A2N = A1B1 c1d1.. where all elements not written out are zero... CN DN calculate its determinant an bn .. .. .. A2n = a1b1 c1d1 ... where the unwritten elements are zero .. .. cn dn Calculate its determinant The prototype of the title probably knows that the title is a bit misplaced

Anbn... A2N = A1B1 c1d1.. where all elements not written out are zero... CN DN calculate its determinant an bn .. .. .. A2n = a1b1 c1d1 ... where the unwritten elements are zero .. .. cn dn Calculate its determinant The prototype of the title probably knows that the title is a bit misplaced

Expand the determinant according to the first line, and then expand it again
A2n = andnA2(n-1)+(-1)^(1+2n)bn(-1)^(2n-1+1)cn
= (andn-bncn)A2(n-1)
Recursion
A2n = (andn-bncn)A2(n-1)
= (andn-bncn)(an-1dn-1 - bn-1cn-1)A2(n-2)
= ...
= ∏(aidi-bici)

Let two groups of real numbers A1, A2, B1, B2, then (A1B1 + a2b2) ^ 2 ≤ (A1 ^ 2 + A2 ^ 2) (B1 ^ 2 + B2 ^ 2) if and only if the equal sign holds

Let a = (A1, A2, A3), B = (B1, B2, B3), and let a * b = max (A1B1, a2b2, a3b3). If a = (x-1, x-1,1), B = (1, X-2, x-1), and a * b = X-1, then the value range of real number x is_______

This kind of problem is the easiest to do, and it doesn't need to use your brain. Focus on the formula "a * b = max (A1B1, a2b2, a3b3)", that is, multiply the corresponding elements, and then find out according to the gourd. How to get the result? According to the three elements in the max (n, P, q), corresponding to the rectangular coordinate system, draw the graph. Let X-1 be the highest in a certain interval
As long as you can understand the important formula, the following questions are all the knowledge points you have learned a long time ago. When you see this kind of problem, don't be afraid. You don't need to recite the formula. What a good thing. I hope you can overcome the fear of this kind of problem as soon as possible

If the inequality | 2A ‐ 1 | ≤| x + 1 ／ x | holds for all non-zero real numbers x, then the value range of real number a is constant

|X+X\1|=|X|+|X\1|≥2
The inequality | 2a-1 | ≤| x + 1 / X | holds for all non-zero real numbers X
It is equivalent to | 2a-1 | ≤ 2
-2≤2a-1≤2
-1≤2a≤3
-2\1≤a≤2\3