A kind of children's story book was delivered to the bookstore. It sold 30% on the first day, and 120% on the second day, 30 more than the first day. How many of these story books were delivered to the bookstore?

A kind of children's story book was delivered to the bookstore. It sold 30% on the first day, and 120% on the second day, 30 more than the first day. How many of these story books were delivered to the bookstore?

30% × 120% - 30%, = 30% × 6%, = 500 copies; a: there are 500 copies of this kind of story books from the bookstore

What is the integral to the square of E, as long as the result,

The original function of this integral can not be expressed by elementary function, which has been proved by predecessors, so there is no answer

O is the outer center of the triangle ABC, ab = 2, AC = 2, and the angle BAC is 120 degrees. If Ao vector = XAB vector + YAC vector, then x + y =?

I think you should draw a picture first. The outer center is the center of the circumscribed circle
Ao vector = x = AB vector + AC vector, then x + y = 2

What is the relationship between limit and derivative
I know that derivative is a tool to find the limit, but why can derivative find the limit? Derivative is a slope of the curve. How can we find the limit by finding the slope?

This can only be used in some special cases such as 0 / 0, because it can be expressed by its derivative plus a high-order infinitesimal

Solve the equation x-0.5x = 15 x-0.8x = 102.5x + 2x = 9

0.5x=15 x=30

The solution set of quadratic inequality MX ^ 2 + MX + n > 0 is {x | - 2

Your question is wrong We can't work out the specific value of M, N, only 2m + n = 0, M

Help press the calculator: arctan (3 / 5.1) equal to

30.46554492
= 30°27‘56’‘

Given that a is the root of the equation x ^ 2 + BX + a = 0, and a ≠ 0, find the value of a + B
The process should be more detailed

Substituting a into the equation, we get:
a^2+ba+a=0
A (a + B + 1) = 0, divided by a
a+b+1=0
a+b=-1

If the coefficient of X in the expansion of (AX + 1) ∧ 5 is known to be 10, then a is a real number

The general term is
C(5,r)(ax)^(5-r)·1^r
=C(5,r)a^(5-r)x^(5-r)
5-r=3
The solution is r = 2
C(5,2)a^3=10
The solution is a = 1

1/2*2/3*3/4…… *2005 / 2006 (simple operation)

The denominator of the former and the numerator of the latter of the two adjacent terms can be eliminated
1/2*2/3*3/4…… *2005/2006
=1*(1/2*2)*(1/3*3)*...*(1/2005*2005)*1/2006
=1/2006
If you still have questions, please ask!