Make a few questions super easy math .

1. Find 1 (1 1991 + 1 1992 + 1 1993 +...1 2003 + 1 2004).

Since 1 1991> 1 1992> 1 1993....

Let t = 1 1991 + 1 1992 + 1 1993 + ...1/2003+1/2004

So t>1 2004+1 2004+...1/2004=14/2004=7/1002

So 1 t< 1002 7

t<1 1991+1 1991+1 1991+...1/1991+1/1991=14/1991

So 1 t<1991 14

Because 1002 7<143, 1 t <143

Again 1991 14>142, so 1 t>142

From the above, we can see that the integer part of 1 t is 142

2+2^2+3^2+..n 2 = (2n + 1) * (n + 1) * n 6 ———the problem will be said tomorrow).

The formula for the sum of squares of natural numbers, which can be proved using the cubic variance formula.

This formula is chaotic, the denominator is increasing in the front, and how is there no 1994 in the back?

How did the molecule pop up with a 2?

You didn't understand the rest of your question, only one.

The square of 1 plus the square of 2 is added to the square of n.

1^2+2^2+3^2+..n^2=n(n+1)(2n+1)/6

Answer: 3 (1-3 n) can be split first, 3 (1-3 n) = 3-3 (n+1).

Then divide by -2.

I can't figure out how this came to be the formula at the bottom.

First, 3 (1-3 n) can be separated, 3 (1-3 n) = 3-3 (n+1).

Then divide by -2.

The first is the denominator, 1-3=-2. This is a direct calculation.

The numerator multiplies 3 in parentheses. And then there's the following result. There is nothing difficult about this.

1.Let the cost price be x, x=7502Let its cost be x

List price = (1+

3.4.(1) Revenue is x

2) 3) According to Engel's coefficient, (*hee-hee......

5.The area of the square and circle is set to a and b respectively

1-3/4)a=(1-6/7)b

a/b=4/7