People's education press ninth grade volume II mathematics exercise 26.3, question 5, please Throw a small ball from the ground vertically. The relationship between the height of the ball H (unit m) and the movement time t (unit s) of the ball is h = 30t-5t. When the movement time of the ball is, the ball is the highest? What is the maximum height in the movement of the ball? No, I've written down all the original questions

People's education press ninth grade volume II mathematics exercise 26.3, question 5, please Throw a small ball from the ground vertically. The relationship between the height of the ball H (unit m) and the movement time t (unit s) of the ball is h = 30t-5t. When the movement time of the ball is, the ball is the highest? What is the maximum height in the movement of the ball? No, I've written down all the original questions

If the relation is a linear function, there is no solution
If the relation is h = 30t ^ 2 - 5T, the opening is upward, and there is no solution
If the relation is h = 30t - 5T ^ 2, the opening is downward and there is a solution
h=5t（6t-1）=0
t1=0 t2=1/6
When t = (T1 + T2) / 2 = 1 / 12s, the maximum value is obtained
h=355/144m

The range of function f (x) = x2 + X + 1x2 + 1 is___ ．

From the function f (x) = x2 + X + 1x2 + 1, we can get [f (x) - 1] · x2-x + F (x) - 1 = 0 (1). When f (x) = 1, we can get x = 0, which satisfies the condition. When f (x) - 1 ≠ 0, according to the formula (1), we can get the discriminant △ = 1-4 [f (x) - 1] 2 ≥ 0, we can get 4F2 (x) - 8F (x) + 3 ≤ 0, and the solution is 12 ≤

Simple calculation of 14 × 13 of 31 + 17 × 13 + 23 of 31
emergency

14/31 X 13 + 17/31 X 13 + 23
= 13 X 14/31 + 17/31 X 13 + 23
= 13 X (14 + 17) / 31 + 23
= 13 X 31/31 + 23
= 13 + 23
= 36

In physics of the first year of senior high school, two examples about displacement are solved, using the formula: S = 1 / 2 (V0 + VT) t

Write the question, I don't see the question, how to answer

Can space rectangular coordinate system XYZ be taken at will
Do you have to follow the right-hand rule? If it's not the right-hand rule, will it be wrong?

If you change the name of x-axis and y-axis, you will not follow the right-hand rule, but the result must be right

Is the volume of water larger than that of ice?
All the water in a bucket forms ice, and the ice surface is just level with the bucket mouth. At this time, the total mass of the bucket and ice is 22 kg. When all the ice turns into water, you need to pour 2 liters of water into the bucket, and the water surface is just level with the bucket mouth. Ask about the volume and mass of the bucket [label: bucket, bucket, knot]

It must be ice. The density of ice is smaller than that of water. After freezing, the volume of ice with the same mass is larger than that of water!

The formula of pulley block: F = g / N. if the weight of pulley is considered, how should the formula be rewritten?

A:
In ideal case (the weight of moving pulley, friction and rope are all 0 and the lifting speed is uniform): F = g / n
If only the weight of moving pulley is considered: F = (G + G moving) / n
If we consider all the factors in practice: F = g / (η n)

Why is lne multiplied by e-ln1 equal to e
The problem of Senior Mathematics in the entrance examination

lne=1
ln1=0
lne×e-ln1
=1×e-0
=e

What time is eleven minus eight forty

2:20

Natural numbers (except 0) can be divided into (), () and () according to the number of factors~

Prime (the factor is 1 and itself), composite (there are other factors except 1 and itself), 1 (there is only one factor of its own)