Question

1,Найдите значение выражения 4 - 5tg2x · cos2x, если sinx = 0,2. 2,Камень брошен вертикально вверх. Пока камень не упал, высота, на которой он находится, описывается формулой h(t) = -5t2 + 18t (h - высота в метрах, t – время в секундах, прошедшее с момента броска). Найдите, сколько секунд камень находился на высоте не менее 13 метров.3,Двое рабочих, работая вместе, могут выполнить работу за 72 дней. За сколько дней, работая отдельно, выполнит эту работу первый рабочий, если он за два дня выполняет такую же часть работы, какую второй – за три дня?

Answer 1

3) A=(P1+P2)*72  P-производительность А-работа=1

A1=P1*2  A1-часть работы

A1=P2*3   P1/P2=3/2   P2=2P1/3

A=(2P1/3+P1)*72

A=P1*x

x=5*P1*72/3*P1=120 дней 

Answer 2

1. Значение выражения 4 - 5tg2x · cos2x, если sinx = 0,2:

To find the value of the expression 4 - 5tg2x · cos2x, we need to substitute the given value of sinx = 0.2 into the expression. However, we don't have the value of x, so we cannot directly calculate the expression.

If you have any additional information or constraints related to the value of x, please provide it so that I can assist you further.

2. Время, которое камень находился на высоте не менее 13 метров:

The height of the stone thrown vertically upward is given by the formula h(t) = -5t^2 + 18t, where h represents the height in meters and t represents the time in seconds since the stone was thrown.

To find the time the stone was at a height of at least 13 meters, we need to solve the equation h(t) >= 13.

Let's set up the equation and solve for t:

-5t^2 + 18t >= 13

To solve this quadratic inequality, we can first set it equal to zero:

-5t^2 + 18t - 13 >= 0

Now, we can factorize the quadratic equation:

(-5t + 13)(t - 1) >= 0

To find the values of t that satisfy the inequality, we need to consider the sign of each factor:

-5t + 13 >= 0 --> t <= 13/5 t - 1 >= 0 --> t >= 1

Since we are looking for the time when the stone was at a height of at least 13 meters, we need to consider the intersection of these two conditions:

1 <= t <= 13/5

Therefore, the stone was at a height of at least 13 meters for a duration of between 1 second and 13/5 seconds.

3. Время, за которое первый рабочий выполнит работу отдельно:

Let's assume that the total work to be done is represented by the value 1 (or 100%).

If two workers can complete the work in 72 days, then their combined work rate is 1/72 of the total work per day.

Let's denote the work rate of the first worker as R1 (in terms of the total work per day) and the work rate of the second worker as R2.

According to the given information, the first worker completes the same portion of work in 2 days as the second worker does in 3 days.

We can set up the following equation based on the work rates:

2R1 = 3R2

Since the combined work rate of both workers is 1/72, we can also write:

R1 + R2 = 1/72

Now, we can solve these two equations to find the individual work rate of the first worker, R1:

2R1 = 3R2 --> R1 = (3/2)R2

Substituting this into the second equation:

(3/2)R2 + R2 = 1/72

Multiplying both sides by 2 to eliminate the fraction:

3R2 + 2R2 = 1/36

5R2 = 1/36

R2 = 1/180

Now, we can find the time it takes for the first worker to complete the entire work individually by using the work rate:

R1 = (3/2)R2 = (3/2)(1/180) = 1/120

Since the first worker's work rate is 1/120 of the total work per day, it will take him 120 days to complete the work individually.

Therefore, the first worker will complete the work individually in 120 days.