Math masters, please come in

1 Because k1=1 k2=5 k3=17 is proportional to the series, (a1+4d) 2=a1(a1+16d), 12a1d=16d 2, d=3a1 4, q=a5 a1=(a1+4d) a1=

4a1/a1=4

So kn=4 (n+1).

2 Sum k1+k2+...kn

Because kn is a series with 1 as the first term and 4 as the common ratio.

So Sn=a1(1-q n) (1-q) =(a1-an*q) (1-q) (n1).

sn=（1-4^n）/1-4

4^n-1/3

1 Because the high line of the cone is 6 and the number 3. then its bus bar is 12. The base radius is 6. So its side area is RL=6*12* =72and its base area is *6*6=36Therefore, its surface area is 108.

1.Let the bottom diameter of the cone be R and the bus bar L. According to the height and axial cross-section are regular triangles, R=6 cm, L=12 cm, and the conic surface area formula S=;

2.According to the side area formula S1=

The base area formula S1= is obtained to obtain R=2, L=4, so that the angle is 60 degrees;

3.To cover a chimney with a diameter of 15 cm, then at least the radius of the bottom of the conic used to cover it is required to be equal to the radius of the base of the original column, i.e.; Let the bottom diameter of the cone be R, and the circumference of the bottom of the cone made by the fan can be obtained according to the existing conditions as the arc length of the fan = 2*, and R = < can be obtained, so the chimney cannot be covered;

4.In this problem, you can first find the conical bus AD, and the bottom diameter of the cone R is the trapezoidal height H, then the bus square = H square + AE square = 40 * 40 + [(130-50) 2]*[130-50) 2] = 2 * 40 * 40, and the bus = 40 * root number 2 can be obtained

Root number 3 = 2 branch root number 3 times x (SIN60) x = 12 S = radius of the cone) = 1 2 * 144 = 72

2.Cone radius square = 4 factions 2 factions, R = root number 2, L bus = 8 factions 2 factions with number 2 = 2 root number root number 6

X=40, AD=40, S=2Send. 40*50+ faction 3

Side view of the cone: The surface area of the cone = the bottom area + the side area, i.e. S = r 2 + ra (Note: a = busbar).

Question 1: According to the regular triangle, you can find the radius r of the bus bar a and the bottom circle, and then substitute it into the above formula.

Question 2: The area of the bottom circle can be obtained from the title, the radius r of the bottom circle can be obtained, and the bus bar a can be obtained according to the side area formula.

Question 3: S fan (n 360) R 2 (n is the degree of the central angle of the circle, R is the radius of the base circle).

According to the area formula of the above two questions, you can find the radius r of the circle at the bottom of the cone, and then compare it with the radius of the chimney.

Question 4: First, find the conical bus AD, and the bottom diameter of the cone R is the trapezoidal height H, then the bus square = H square + AE square.

According to the formula of conical side surface area and cylindrical side surface area, the total surface area = 2 conical side area + 1 cylindrical side surface area can be obtained.

These four questions are all about the application of formulas, so I only give ideas for solving the problems, and then I believe that you can solve them by yourself, so that the knowledge is profound. Therefore, it is necessary to understand the derivation of formulas more, so that there will be no problem with this kind of problem. Come on!!

Question 1: According to the regular triangle, you can find the radius r of the bus bar a and the bottom circle, and then substitute it into the above formula.

Question 2: The area of the bottom circle can be obtained from the title, the radius r of the bottom circle can be obtained, and the bus bar a can be obtained according to the side area formula.

Question 3: S fan (n 360) R 2 (n is the degree of the central angle of the circle, R is the radius of the base circle).

According to the area formula of the above two questions, you can find the radius r of the circle at the bottom of the cone, and then compare it with the radius of the chimney.

Question 4: First, find the conical bus AD, and the bottom diameter of the cone R is the trapezoidal height H, then the bus square = H square + AE square.

According to the formula of conical side surface area and cylindrical side surface area, the total surface area = 2 conical side area + 1 cylindrical side surface area can be obtained.

I know how to solve math problems in junior high school, but what about the problems?

Give points! Hee-hee

I didn't give a question, so I had to get the question out.

Minutes to get from home to school, it takes 40 minutes to walk, 1 40 minutes per minute to walk, 16 minutes to ride a bike, 1 16 minutes to ride a bike to school, 5 minutes to ride, 5 minutes to ride, 11 16 of the total distance remaining, the time it takes to walk = (11 16) (1 40) = minutes to share minutes from home to school.

The distance from school to home is X

The bike speed is X 16 and the walking speed is X 40

Some time ago, the bicycle went X 16 * 5, and there is X-X 16 * 5 left, then the time spent in the rear section (X-X 16 * 5) (X 40) = 55 2, so the total time is 55 2 + 5 = minutes).

Minute. You have to use a formula to calculate, it's troublesome.