How to change sine function into cosine function For example, u = 40sin (2 π f-60 °), how to change cos function

How to change sine function into cosine function For example, u = 40sin (2 π f-60 °), how to change cos function

How can sine function become cosine function
As long as the initial phase of the sine function is reduced by 90 degrees (that is, the sine vector is rotated clockwise by 90 degrees), the cosine function equivalent to the original function is obtained
u=40sin（ωx-60°）==>u=40sin（ωx-60°-90°）=40cos（ωx-150°）
Or the initial phase of the sine function is increased by 90 degrees (that is, the sine vector is rotated 90 degrees counterclockwise) to obtain the cosine function equivalent to the original function
u=40sin（ωx-60°）==>u=40sin（ωx-60°+90°）=-40cos（ωx+30°）

The circumference of a rectangle is 25.12cm, the width is 6cm and the length is 5cm___ Cm, the area is___ cm2．

25.12 △ 2-6, = 12.56-6, = 6.56 (CM), 6.56 × 6 = 39.36 (cm2), answer: length is 6.56cm, area is 39.36cm2

What's the 1 / 3 power of 27? What's the integer?

Because 27 = 3 * 3 * 3
So the 1 / 3 power of 27 is 3, which is to find the cube root of 27

Xiao Wang's family of four, two aunts and their family travel to a scenic spot. The charging standard of this scenic spot is as follows: 50 yuan per person for no more than 5 people. If more than 5 people, the ticket will be 60% off. As a result, it costs 10 yuan less than going alone, so the total number of people who go to the two aunts is ()
A. 3B. 4C. 5D. 6

Suppose that the number of people who go to two aunts' houses is X. according to the meaning of the question, we get: 50 (x + 4) - 50 × 5-50 (x + 4-5) × 60% = 10 (x + 4). Solving the equation, we get: x = 6, so we choose: D

In rectangular paper ABCD, ab = 3, ad = 5. As shown in the figure, fold the paper so that point a falls at a 'on the edge of BC, and the crease is PQ. When point a' moves on the edge of BC, the end point P.Q of the crease also moves. If the limiting points P and Q move on the edge of AB and ad respectively, the maximum distance that point a 'can move on the edge of BC is ()
A. 1B. 2C. 3D. 4

As shown in Figure 1, when point d coincides with point Q, according to the folding symmetry, we can get a ′ d = ad = 5. In RT △ a ′ CD, a ′ D2 = a ′ C2 + CD2, that is 52 = (5-a ′ b) 2 + 32, we can get a ′ B = 1. As shown in Figure 2, when point P coincides with point B, according to the folding symmetry, we can get a ′ B = AB = 3, ∵ 3-1 = 2, and the maximum distance that a ′ can move on the edge of BC is 2

A pen is 5 yuan and a pencil is 1.5 yuan. Xiao Ming bought 6 pens and pencils with 16 yuan

5*6=30
30-16=14
14/(5-1.5)=4
6-4=2
A: Xiao Ming bought two pens and four pencils

Xiaoming walks 78 meters per minute. The distance from the Grand Theater to the school is three times that from Xiaoming's home. How far is the distance from Xiaoming's home to the Grand Theater?

There is something wrong with this topic, because the location of the three locations is not clear, and the questions are not clear
Let's take a look at the two simplest cases
1、
Three points in a straight line, the school in the middle
Distance from home to the Grand Theater = 78 * 15 * 4 = 4680m
Time from home to the Grand Theater = 15 * 4 = 60 minutes
Time from school to Grand Theater = 15 * 3 = 45 minutes
2、
Three points in a straight line, home in the middle
Distance from home to the Grand Theater = 78 * 15 * 2 = 2340 meters
Time from home to the Grand Theater = 15 * 2 = 30 minutes
Time from school to Grand Theater = 15 * 3 = 45 minutes
If the three points are not in a straight line,
It can only be said that,
The distance from home to the Grand Theater is between 2340m and 4680m
The time from home to the Grand Theater is between 30 minutes and 60 minutes
The time from school to the Grand Theater is 45 minutes

A cuboid is 5cm long, 5cm wide, 5cm high and 4cm high. The cuboid has two faces which are () shaped, and the area of () faces is equal at most. The surface area of the cuboid is（

A cuboid is 5cm long, 5cm wide, 5cm high and 4cm high. The cuboid has two (square) faces with equal area at most. The surface area of the cuboid is 2 (5 * 5 + 4 * 5 * 2) = 130cm2

2. It was originally planned to take 5 hours and 30 minutes for Liping to ride from her home to the county. Due to the uneven road of 3.6 kilometers on the way, the speed of this section of the road was slower than before
2. It was originally planned to take 5 hours and 30 minutes for Liping to ride from her home to the county town. Due to the uneven road of 3.6 km on the way, the speed of this section was 3 / 4 of the original speed, so she arrived 12 minutes late. Liping's home is () km away from the county seat

The distance is equal and the speed is inversely proportional to the time
If the speed is 3 / 4 of the original, the time will be 4 / 3 of the original, 1 / 3 more than planned
The planned time is 12 △ 1 / 3 = 36 minutes = 3 / 5 hours
Planned speed = 3.6 △ 3 / 5 = 6 km / h
Distance = 6 × 5.5 = 33 km

A practical problem in life
Two people use a car (taxi) because it is burning natural gas, there is a problem of insufficient air pressure, so it is calculated according to the kilometers run by each person every day, and the monthly settlement is made with a card to recharge together. The key data are (kilometers per person every month) (recharge number per person) (card balance) (last month balance) The first month is OK. The second month, the card balance and last month's balance are not accurate. Provide data on site
It's better to have a formula

After the first month's calculation, the balance in the card must be clearly divided into a balance and B balance;
A recharge amount of this month - a amount that should be recharged in this month = a balance at the end of this month;
B current month recharge amount - B current month should be recharged amount = B balance at the end of this month;
Card balance = a balance at the end of this month + B balance at the end of this month;
At the end of the second month,
A balance of last month + a recharge amount of this month - a amount that should be recharged in this month = a balance at the end of this month;
B balance of last month + B recharge amount of this month - B amount that should be recharged in this month = B balance at the end of this month;