Here are two circles. The sum of their areas is 1991 square centimeters. The perimeter of the small circle is 90% of that of the big circle (as shown in the figure). Q: what's the area of the big circle?

Let the area of the big circle be x square centimeter, then the area of the small circle is (90%) 2 = 0.81x square centimeter, & nbsp; & nbsp; & nbsp; X + 0.81x = 1991, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; 1.81x = 1991, 1.81x △ 1.81 = 1991 △ 1.81, & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; X = 1100. A: the area of the big circle is 1100 square centimeter

Taking AB and AC of Δ ABC as sides, make square ABDE and ACGF outwards, ah as the middle line on BC, make an ⊥ BC at point n, extend Na intersection EF at point m, and prove: EM = MF = ah

Because BH = HC, HP = ah, ABPC is a parallelogram, and CP = AB, ∠ ACP + ∠ BAC = 180 ° can be obtained

Know the chord length of 69 meters, the distance between the arc and the chord is 5.3 meters, how to calculate the arc area!
It's the distance between the middle point of the string and the arc is 5.3 meters. I didn't express it accurately in a hurry!
Radius 5.9 meters?

Do you have these statements about "distance between arc and chord" and "calculation of arc area"

The problem of summation of sequence of higher one
Sequence summation 1 + 4 + 12 + 32 + +n*2^(n-1)

Let s = 1 * 2 ^ 0 + 2 * 2 + 3 * 2 ^ 2 +. + n * 2 ^ (n-1)
2S=1*2+2*2^2+3*2^3+.+n*2^n
S-2s = (2 ^ 0 + 2 ^ 1 + 2 ^ 2 +... + 2 ^ (n-1) - n * 2 ^ n = 1 * (2 ^ n-1) / (2-1) - n * 2 ^ n
That is, the original formula = s = n * 2 ^ n-2 ^ n + 1

English translation
Add the question of "under what circumstances did the author compose the poem"!

A thread is in my fond mother's hand moving.For her son to wear the clothes ere leaving.With her who...

Second grade mathematics inverse proportion function application online and so on!
Xiaoming's family just bought a new house with an area of 108m & sup2; this year, and now they need to lay floor tiles
(1) The functional relationship between the required number of tiles N and the area of each tile s
(2) In order to be beautiful, xiaomingjia decided to use 60cm × 60cm floor tiles and composite wood floor, and the use ratio of floor tiles and composite floor is 3:2. How many pieces of these two materials are needed?
Ask to use inverse function, thank you

I'm drilling under the bed. I have no pen and paper, so I'll give you an idea
(1)N=108/S
(2) First, we flatten 108m into cm. To get a. then we use a / 66cm * 66cm. To get B. then we multiply 3.2 to get the number of bricks
A. B refers to the result
Tomorrow?

The surface area of a cuboid is 78 cm, the bottom area is 15 square cm, and the perimeter of the bottom area is 16 cm

The lateral area is 78-2 * 15 = 48 (CM & # 178;)
Bottom radius 16 / 4 = 4 (CM)
Height (48 / 4) / 4 = 3 (CM)
V = bottom * height = 15 * 3 = 45 (CM & # 178;)

If Tan θ = (root 3) / 3, then cos ^ 2 θ - sin (θ + π / 6) cos θ
23：15

In this case, the original formula = cos # 178; therefore, the original formula = cos \35; 178; therefore, the original formula = cos \# 178; therefore, the original formula = cos \\35; 178; therefore, the original formula = cos \\35; 178; so, the original formula = cos \\35; 178; therefore, the original formula = cos \\\\\\; therefore, the original formula = cos \

Here are two circles. The sum of their areas is 1991 square centimeters. The perimeter of the small circle is 90% of that of the big circle (as shown in the figure). Q: what's the area of the big circle?