Ask an English word Park raofet, What word is it? How to write it in English,

Ask an English word Park raofet, What word is it? How to write it in English,

It should be profit
Because it sounds like "Park Rao Fei Te"
It means "profit, advantage"
It's good for, good for, profit for

In the arithmetic sequence {an}, the sum of its first n terms is SN. If S12 = 21, then A2 + A5 + A8 + a11 equals ()
A. .5B. .6.C. 7.D. .10

In the arithmetic sequence {an}, the sum of its first n terms Sn = n (a1 + an) 2, so S12 = (a1 + A12) × 122 = 21, then a1 + A12 = 72, and a1 + A12 = A2 + a11 = A5 + A8, so A2 + A5 + A8 + a11 = 2 (a1 + A12) = 2 × 72 = 7

Find the total differential of F (x, y) = sin (XY + X + y)?

f'x=cos(xy+x+y)*(y+1)
f'y=cos(xy+x+y)*(x+1)
dz=f'xdx+f'ydy=cos(xy+x+y)*[(y+1)dx+(x+1)dy]

The two classes went to visit the museum 30 kilometers away from the school. But there was only one pick-up car in the school. The speed was 45 kilometers per hour, and the students walked 5 kilometers per hour. In order to make the two classes arrive as soon as possible, they set out from the school at 8 a.m?

If the bus can deliver one shift at a time, it will take 30 / 45 = 2 / 3 hours for the first one to arrive, and the second one has already gone 5 * 2 / 3km
Then the second bus takes (30-5 * 2 / 3) / (45 + 5) = 8 / 15, and the second bus takes 5 * 8 / 15km. At this time, the second bus is 30-5 * 2 / 3-8 * 5 / 15 = 24km away from the terminal, and it takes 24 / 45 to reach the terminal
All in all, it took 2 / 3 + 8 / 15 + 24 / 45 = 26 / 15 hours for the above-mentioned bus. Because it started at 8 o'clock, it was 8 + 26 * 60 / 15, that is 9:36

How many pairs of vertex angles are there at most when two lines intersect each other

4038090

Let z = xsin (XY), then what is Z / &; y

Let's take x as a constant,
∂z/∂y=xcos(xy)*(xy)'=xcos(xy)*x=x^2 * cos(xy)

When the crystal melts, the internal energy does not change, but when the ice melts, the internal energy increases. Why?

When a crystal melts, it needs to absorb heat. The internal energy increases, but the temperature remains the same. The reason is that the increased internal energy is used to change the state (volume) of matter

I have a question about proving Newton Leibniz formula
The increment of each inter cell function is Δ Y1, Δ Y2 Δ YN, obviously
f(b)-f(a)=Δy1+Δy2+… +Δyn
=f′(x1)Δx1+o(Δx1)+f′(x2)Δx2+o(Δx2)+… + f′(xn)Δxn+o(Δxn)
=f′(x1)Δx1+o1Δx1+f′(x2)Δx2+o2Δx2+… + f′(xn)Δxn+onΔxn
=f′(x1)Δx1+f′(x2)Δx2+… + f′(xn)Δxn+o1Δx1+… +onΔxn,
Obviously, Δ X1 + Δ x2 + +When the length of each subinterval Δ Xi → 0, O1 → 0, O2 → 0 It is easy to prove that O1 Δ X1 + +On Δ xn → 0
f′(x1)Δx1+f′(x2)Δx2+… + f′(xn)Δxn→f(b)-f(a)
o1Δx1+… +On Δ xn here when Δ Xi → 0 seems to have infinite numbers, how can we prove O1 Δ X1 + +onΔxn→0?

Which formula is this? I have never seen Newton Leibniz formula like this. I have only seen Newton Leibniz formula in solving definite integral, and the proof of this formula is not what you gave

The left and right limits of the sign function SGN x at point x = 0 are discussed

The left limit of SGN x at point x = 0 is - 1
The right limit of SGN x at point x = 0 is 1
The left and right limits of signed function SGN x at point x = 0 are not equal

How many degrees, minutes and seconds is 31.78 degrees

0.78 degrees = 0.78 * 60 = 46.8 points
0.8 min = 0.8 * 60 = 48 s
31.78 degrees = 31 degrees 46 minutes 48 seconds
The main reason is that the progression rate of degrees, minutes and seconds is 60. When converting, multiply 60 every time to get the integral part. Do you understand?