If you ask a math question, there are x science and technology books, four times as many story books as science and technology books, and 450 story books,

If you ask a math question, there are x science and technology books, four times as many story books as science and technology books, and 450 story books,

There are x science and technology books and 4x story books
4x - x = 450
3x = 450
x = 450/3
x = 150
x = 150
4x = 600
A: there are 150 science and technology books and 600 story books

A uniform ladder with length of L and weight of W is placed against the wall, as shown in the figure. The lower end of the ladder is connected with a spring with stiffness coefficient of K. when the ladder is placed vertically against the wall, the height of the ladder is 1,
The spring is in the natural length. Both the wall and the ground are smooth. When the ladder is at an angle a to the ground and in a state of equilibrium, the relationship between W, K, l and a is as follows________________

The method is basically fixed
First, the stress analysis is done, the ground supporting force N1 = w, the wall supporting force N2 = spring pressure = k * L * cosa
Then take the ground support point (or wall support point) as the reference point, do the moment balance equation
N2*l*sina=W*l/2*cosa
It is concluded that w = 2K * L * Sina

How to add four arithmetic symbols in the middle of four sixes to equal six

(6-6)×6+6=6

A 20n object slides horizontally to the right under the action of a 4N horizontal pull to the right to determine the dynamic friction coefficient between the object and the table

If sliding to the right at a constant speed on the horizontal plane: 20u = 4, u = 0.2 can be obtained; according to this limit value, u ≤ 0.2 can be deduced

It is known that the sum of the first n terms of the arithmetic sequence {an} is Sn, and satisfies A2 + A4 = 6, S7 = 28
Let {BN} = (2Sn + 48) / N, what is the minimum term of the sequence {BN}, and find out the value of the term?

A2 + A4 = 2A3 = 6, then:
a3=3
S7 = [7 (a1 + A7)] / 2 = (7 / 2) (a1 + A7) = (7 / 2) (2a4) = 7a4 = 28, then:
a4=4
Then: D = a4-a3 = 1
So, A1 = 1, d = 1, then: an = n
So, Sn = [n (n + 1)] / 2
The results are as follows
bn=[n(n＋1)＋48]/n=n＋1＋(48/n)
If f (n) = n + (48 / N), then f (n) decreases on (0, √ 48) and increases on (√ 48, + ∞), then the minimum value of F (n) is f (6) = 14, so the minimum value of BN is B6 = 15

If the displacement of an object moving in a straight line with uniform acceleration from rest is 8 m in the first 2 s, then
(1) Displacement in the first 10 s (2) displacement in the 10th s (3) average velocity in the first 6 s ==

A = V / T = 8m / S / 2S = 4m / S ^ 2 1, x = VT + at ^ 2 = 0 + 4m / S ^ 2 x [10sx10s] = 400m 2 v = at + V0 = 4m / S ^ 2 x10s + 0 = 40m / s, so it's 40m [the tenth second is a moment, how can we calculate the displacement?] 3 x = VT + at ^ 2 = 0 + 4m / S ^ 2 x [6sx6s] = 144m v = s / T = 144m / 6S = 24m / S

Xiaohua's father takes one day off every eight days, and his mother takes one day off every five days. On May 28 this year, his father and his mother take a rest at the same time, so what's the next time______ Rest at the same time

9 = 3 × 3, 6 = 3 × 2, the least common multiple of 9 and 6 is 3 × 3 × 2 = 18, that is, 18 days later, his father and mother rest at the same time. 31-28 = 3, 18-3 = 15; a: then the next time to rest at the same time on June 15

When someone takes a train, he sees a two digit number (unit: kilometer) written on the first milestone, and the sum of its two digits is 7. After one hour, he sees that the second milestone happens to be the number of the first milestone interchanged. After another hour, he sees a three digit number written on the third milestone, This three digit number is just the two digit number in the first milestone. Add a zero in the middle. What's the speed of the train?
——
The problem in the exercise book will set up an equation, that is, the second block minus the first block = the third block minus the second block, but the equation is too complex to calculate an integer Depressed Hope to have a simple algorithm, but we must use the equation to solve it. Choose one of one variable once and one variable twice. Typing is very tiring

The two digit sum of 7 is: 16 61 25 52 34 43 7061-16 = 4545 + 61 = 106. Let the number on one digit be x, and the number on ten digit be 7-x. the original two digit sum is: 10 (7-x) + x = 70-10x + x = 70-9x. After the digit exchange, add a 0:100 (7-x) + x = 700-100x + x = 700 -

If x = 1 is the solution of the linear equation x & # 178; + kx-3 = 0, then the value of K is?

X = 1
1+k-3=0
k=2

The following equations are solved by the elimination method
1,y=x-2,2x+y=10 2,x-5y=0,3x+2y=17 3,2x-y=5,3x+4y=2
4,3x-2y=-1,2x+3y=8

1, y = X-2, (1) 2x + y = 10 (2) (1) substitute (2) to get: 2x + X-2 = 103x = 10 + 2x = 12 / 3x = 4 substitute (1) to get: y = 22, x-5y = 0, (1) 3x + 2Y = 17 (2) substitute (1) to get: x = 5Y substitute (2) to get: 3 × 5Y + 2Y = 1717y = 17Y = 1 substitute (1) to get: x = 5, 3, 2