This pervert is difficult to deal with. I have done the first two questions for 15 minutes, and there are still 15 minutes left, so I can't attack the third question. Now there is an answer online.

(2) If possible, use a 1(a2) and d directly.

a 1*a3^3=a2^4,a2^2*a4^4=a3^6，

Substitute the root number A2 * A4 2 = A3 3 of the second formula into the first formula.

A2 3 = a1* A4 2 = (A2-D) (A2+2D) 2. Solve, A2 2 = 4/3D 2, A2 two values, one does not satisfy A4 > 0, and the other is not established (actually it is not).

(The answer method is better)

(3) The idea of the answer: Taking D as the independent variable, it is proved that only d=0 holds, which is contradictory.

Homogenize first, and divide a 1 and d in the homogeneous formula by a 1 to become a unary formula.

After that, the parameters n and k are eliminated. The method is to take the natural logarithm in the exponential formula. Then it becomes a unary equation, sets a function and studies the zero point of the function instead.

The train of thought is hard to think, and then the derivative is hard to calculate. But if you have a deep foundation, these are just some routine operations. Huashan Mountain has been a road since ancient times and should be regarded as an accumulation.

How did the landlord do in the exam?