Ask a few high school math questions and hurry up to detail the steps

Solution: Because a(n+1)+2sn 3=1 (1) so a(n+2)+2s(n+1) 3=1 (2) from (1)-(2) a(n+1)-a(n+2)=2a(n+1) 3a(n+1)=3a(n+2).

an} is a proportional series, and the common ratio is 1 3

Because a1 = 1

So the (n-1) power of an=1 3 (which can only be expressed in this way, forgive me) is summed according to the proportional sequence.

sn=(a1-a(n+1))/(1-q)

3 2 (1-1 3 to the nth power).

bn = 2 * (3 2 (1-1 3 to the nth power)) - 1 = 3-1 3 to the (n-1) power.

Note: a(n+1), a(n+2), etc. represent number series, and the computer expression ability is limited, forgive me.

Solution: a(n+1) +2 3 sn = 1 ==> a[n+1] =1-2 3*s[n] -1).

a[n] = 1-2 3*s[n-1] -2)1)-(2).

a[n+1]-a[n] =-2/3(s[n]-s[n-1]) = -2/3 a[n]

a[n+1]/a[n] = 1/3

The series is a proportional series with a common ratio of 1 3, and the general formula is.

a[n] = a[1]*q (n-1) =1 3 (n-1)2, solution: b[n]= 2s[n] -1 --1)b[n+1] =2s[n+1]-1 --2)2)-(1):

b[n+1]-b[n]=2(s[n+1]-s[n]) = 2b[n+1]

b[n+1]=-b[n]

b[1]= 1

The general formula is:

b[n]=(-1)^(n-1)

You can't write this clearly, how do you understand an+1 +2 3 sn = 1? an+1=1-2 3sn a1=1 sn=a1+a2+a3++an when n=1, a2=1 3 when n=2, a3

an+1=1-2/3sn

a1=1sn=a1+a2+a3+..an

When n=1, a2=1 3

When n=2, a3=1 9

When n = 3, a4 = 1 27

Ask for bn and it's about the same as this.

You can't write this clearly.

an+1 +2 3 sn = 1

1;Solution: original formula = -tan60° + sin90° = -3 + 1 = 1- 32: the slag code is used by the double angle formula f(x) = 3 2sin2x + sin2x-1 2 = ( 3 2-1) sin2x-1 2

Therefore, the period of vanity = 2 2 =

There is f(x)=sinx, the abscissa is compressed first, 1 2, the ordinate is unchanged. Then the ordinate expands (3, 2-1) and the abscissa remains unchanged.

Finally, the ordinate is shifted downward 1 2

3: Let the length x width be 20 x, and then the column equation should be known as the least when the mean inequality should be square.

Paint and then compare the magnitude relationships of the respective derivatives.

These 3 questions must be solved by combining numbers and shapes, and as long as you can draw a diagram, you can find the answer.

1 question, 2cos(a+b)=1

It can be seen that a+b=60°

Then c=120° you can find the sine and cosine value of the special horned mammoth. 2, 3 questions haven't thought of yet.

2. Using linear programming, it can be obtained. It's not very good to draw pictures here, so you have to read the book yourself.

3. I didn't expect it yet. But it's also a drawing.

Because it's a series of equal differences.

So a1004 + a1006 = 2a1005

3a1005=3

a1005=1

s2009=a1+a2+..a2009=2009*a1005=2009

Definitely choose B, there is no accident to disturb ......

Scores. 3(4+x+y)=xy+2x+2y+4xy-x-y-8=0

xy=x+y+8

by Cauchy inequality.

x+2)+(y+2)

x+2)+(y+2)]*3/(x+2)+3/(y+2)]x+y≥8xy=x+y+8≥16

Pick D. In fact, considering that this is a multiple-choice question of Li Tong, this type of inequality should know that the equality condition must be x=y, so that x=y can solve x=y=4. This is the right way to do multiple-choice questions ==

If you have a big question, you have to do it honestly.

The choice is right. When the distance from m,n to is equal, the plane is also a set that satisfies the conditions.

If you think that the explanation of the bird circle is not clear enough, please ask.

Wish: Learning progress!

This is the most common trigonometric question in high school, and the exam generally appears in the first question of the big question, which belongs to the basic question type. The main use is to simplify the double angle formula and the auxiliary angle formula, and then find the period according to the minimum positive period formula, and then calculate the maximum value or symmetry axis on the given interval. You can just ask the teacher around you for the specific solution, don't be afraid of being embarrassed.