Everyone, please help, I need this information very much

The idea is wrong, the last term of the squared formula is 2 times the x1*x average.

If x1 and x2, the average is m

then the variance s 2=1 n[(x1-m) 2+(x2-m) 2++xn-m)^2]

That's right, turn him on 1 n [(x1 +x2 +....xn²)-2m(x1+x2+..xn)】+m^2

1 All 13 lg2*5=lg10=1

14 First simplify the brackets in parentheses, so is a to the 6th power.

15 tana = sina cosa = 2 2 = 216 bc = (6-3, 2- -4) = (3, 6) 17 parallel or intersecting.

18.Can't see clearly.

19k=1,b=0

21 a b

A crosses b=a and b=

1. As I walked, I thought, "Where did you read yesterday?" Which book is placed in **? Third row on the left, nice ......”

2. But I'm worried about whether the book will sell out, because I've seen people buy it for a few days, and it seems that there are only one or two copies left yesterday.

3. I stepped into the store, and I was secretly glad that no one was paying attention. Hurriedly opened the book, one page, two pages, and I read greedily like a hungry wolf.

"Greed" refers to the time when you are insatiable and unsatisfied. This sentence uses an extremely vivid metaphor to compare the "I" who is full of the desire to read to a hungry wolf, and the greedy reading page by page is like a hungry wolf eating. It writes about "I" strong desire for knowledge and desire to read.

I'm happy, but I'm also scared of this eavesdropping!

This sentence is the central sentence of the text, which summarizes the various feelings of eavesdropping, and is also a concentrated embodiment of the author's emotions. "I" longed to read, but I couldn't afford to buy it, so I had to "eavesdrop". But the so-called "plagiarism" is nothing more than reading and not buying.

I "feel the wisdom and happiness brought by books in reading, but I am always afraid of being reprimanded and driven away by the clerk or boss, this kind of attraction and addiction to the world in the book, and the worry and tension of the world outside the book, so that the happiness and fear are intertwined, forming a complex and indescribable feeling, which is the taste of eavesdropping."

Sometimes I have to pretend to frown, and from time to time I look at the middle of the street, as if to say, "This rain has caused me not to go back." In fact, my heart shouted with joy, "Bigger! Bigger! ”

This sentence describes the contrast between the sad expression and the happy heart, and it is interesting to write that "I" am very happy to have a good reason to read on a rainy day, and it shows "I" love to read.

I closed the book and swallowed as if I had swallowed all the wisdom before reluctantly putting it back on the shelf.