A batch of story books were delivered to the bookstore. On the first day, they sold 15 bags less than one sixth of these books, and there were still seven eighths left. How many bags are there in this batch of story books? What's sold 1－7/8=1/8 At the same time, it's 15 bags less than 1 / 6 therefore What are the characteristics of these storybooks 15 (1 / 6-1 / 8) = 360 (packet) why divide by 15?

A batch of story books were delivered to the bookstore. On the first day, they sold 15 bags less than one sixth of these books, and there were still seven eighths left. How many bags are there in this batch of story books? What's sold 1－7/8=1/8 At the same time, it's 15 bags less than 1 / 6 therefore What are the characteristics of these storybooks 15 (1 / 6-1 / 8) = 360 (packet) why divide by 15?

1. Because after the first day of sale, there are still seven eighths of them not sold, that is to say, one eighth of them were sold on the first day; 2. The title says that "the first day of sale is 15 packets less than one sixth of these books", that is to say, one sixth of these books plus 15 packets is equal to one eighth of these books, that is to say, one sixth of these books

There are 480 science and technology books and story books in the school. The number of science and technology books is three times that of story books. How many of the two books are there?

The number of story books: 480 △ 3 + 1, = 480 △ 4, = 120; the number of science and technology books: 120 × 3 = 360, or 480-120 = 360; answer: there are 120 story books and 360 science and technology books

The school bought 120 more story books than science and technology books, and the number of story books is five times that of science and technology books?

There are more story books than technology books
5-1 = 4 times
Science and technology books
120 △ 4 = 30
The story book has
30 × 5 = 150

As shown in the figure, the two heights AD and BM of △ ABC intersect at e, connecting EC, ∠ AEB = 105 ° and ∠ bad = 45 °
prove:
（1）AB=2AM
（2）BE=AC
（3）AB-BE=CE
（4）AM-CM=CE

I don't know if you have learned sine theorem and cosine theorem, that is AB / sin ∠ C = BC / sin ∠ a = AC / sin ∠ B
Sin105 ° = sin (60 ° + 45 °) expansion can be calculated, you can assume that the ad side length is 1, and then the length of each side can be calculated, note that the triangle ame is similar to the triangle BDE, and finally each side can be calculated, and then prove
If you have a good foundation, in fact, it's very fast. I've done it, and it can be counted. You have a try first

It is known that P and Q are two points on the parabola x2 = 2Y. The abscissa of points P and Q are 4, - 2 respectively. If the two tangents cross point a, the ordinate of point a is ()
A. 1B. 3C. -4D. -8

∵ P, q are two points on the parabola x2 = 2Y, the abscissa of points P and Q are 4, - 2, ∵ P (4,8), q (- 2,2), ∵ x2 = 2Y, ∵ y = 12x2, ∵ y ′ = x, ∵ tangent equation AP, the slope of AQ, KAP = 4, KAQ = - 2, ∵ tangent equation AP is Y-8 = 4 (x-4), i.e., y = 4x-8, the abscissa of tangent equation AQ is Y-2 = - 2 (x + 2), i.e., y = - 2x-2, so that y = 4x-8y = - 2x-2, ∵ x = 1y = - 4, the ordinate of point a is -4. Select: C

ABCD is a square, which is composed of four small squares. E and F are the midpoint of AD and ab respectively. If the area of △ EFC is 54, then ab=______ ．

Let the small square area be s, then the large square area be 4S, and the area of △ EFC be 4s-2s-0.5s = 1.5s, because 1.5s = 54, then s = 36, so 4S = 36 × 4, = 144, and & nbsp; 12 × 12 = 144. So AB = 12; answer: AB is 12. So the answer is: 12

Given that X1 and X2 are two real roots of the equation x2 + 5x + 2 = 0, then x13 + 23x2 + 5=______ ．

∵ X1 and X2 are the two real roots of the equation x2 + 5x + 2 = 0, ∵ X12 = - (2 + 5x1), X1 + x2 = - 5, ∵ x13 + 23x2 + 5 = - (2 + 5x1) · X1 + 23x2 + 5 = - 2x1 + 5 (2 + 5x1) + 23x2 + 5 = - 2x1 + 10 + 25x1 + 23x2 + 5 = 23x1 + 23x2 + 15 = 23 (x1 + x2) + 15 = 23 × (- 5) + 15 = - 100

We know that four points o, a, B, C in the plane satisfy the vector
Let o, a, B, C be four points on the plane, vector OA + vector ob + vector OC = vector 0, OA * ob = ob * OC = OC * OA = - 1, then the area of triangle is

Because vector OA * vector ob = vector ob * vector OC = vector OC * vector OA = - 1
So vector OA * vector ob - vector ob * vector OC = 0
So the vector ob * (vector OA vector OC) = 0
So the vector ob * vector CA = 0
So vector ob, vector AC
Similarly, vector OA, vector BC, vector OC, vector ab
So o is the center of triangle ABC
Because vector OA + vector ob + vector OC = vector 0
So o is the center of gravity of the triangle ABC
Because the center of gravity coincides with the center of gravity
So the triangle ABC is an equilateral triangle
So vector OA * vector ob = |oa | * |ob | * cos120 ° = - (1 / 2) * |oa | * | ob | = - 1
So | OA | * | ob | = 2
So triangle ABC area = 3 * | OA | * | ob | * sin120 ° = 3 * radical 3

How to multiply polynomials by polynomials? (3 + 1) (3 ^ 2 + 1) (3 ^ 4 + 1) (3 ^ 8 + 1) (3 ^ 16 + 1) - 3 ^ 32 / 2 reward!

Original formula = (3-1) (3 + 1) (3 ^ 2 + 1) (3 ^ 4 + 1) (3 ^ 8 + 1) (3 ^ 16 + 1) / (3-1) - 3 ^ 32 / 2 = (3 ^ 2-1) (3 ^ 2 + 1) (3 ^ 4 + 1) (3 ^ 8 + 1) / 2-3 ^ 32 / 2 = (3 ^ 4-1) (3 ^ 4 + 1) (3 ^ 8 + 1) (3 ^ 16 + 1) / 2-3 ^ 32 / 2 = (3 ^ 8-1) (3 ^ 8 + 1) (3 ^ 16 + 1) / 2-3 ^ 32 / 2 = [3 ^ 32-1] /

In the cube abcd-a'b'c'd ', EF is the midpoint of AA' and CC 'respectively. It is proved that BF is parallel and equal to ed'

It is proved that: take the midpoint g of BB 'and let e be the midpoint of AA' to get ed '/ / which is equal to GC' one
Because f is the midpoint of CC ', BF / / is equal to GC' two
From 1 and 2, BF is parallel and equal to ed '
The proof is complete