There are 13 Science and technology books in our bookcase, half of them are story books, and the rest are comic books. How many are comic books?

There are 13 Science and technology books in our bookcase, half of them are story books, and the rest are comic books. How many are comic books?

1-13-12, = 23-12, = 16

There are 30 story books and 23 comic books in the school library. Comic books are () less than story books. Story books account for ()% of the total number of these two books

(30-23)/30=23.33% 30/(30+23)=56.60%

If the equation 4 ^ x + A2 ^ x + A + 1 = 0 about X has a real solution, the range of a?

Let 2 ^ x = y
Then the original equation is
y^2+ay+a+1=0
If x has a real solution, then y also has a real solution
∴△≥0
∴a^2-4(a+1)≥0
The solution is 2-radical 8 ≥ a or a ≥ 2 + radical 8
At the same time, Y > 0
Then (- A + - radical (△)) / 2 > 0
Solving inequality

The simplest integer ratio of 1:4:0.35 is (), and the ratio is ()

36：7
36/7

Calculation (1 + 3 + 5 +...) +99)-(2+4+6+…… +100)

(1+3+5+…… +99)-(2+4+6+…… +100)
＝（1-2）+（3-4）＋（5-6）＋…… (99-100) (50 groups in total)
＝（-1）+（-1）＋（-1）＋…… (- 1) (50 groups in total)
＝-50

Judge the parity of function f (x) = x power of a - x power of a (a > 0, a ≠ 1) and x power of y = 3 - 1 / 1 + 1 / 2

F (x) is an odd function, f (- x) = a ^ (- x) - A ^ x = - f (x)
1 + 1 / 2 of the x power of y = 3 are odd functions

How many Mu is one square kilometer?

1 m2 = 0.0015 Mu
1 square kilometer = 1000 × 0.0015 = 1.5 mu

What is the square of 1 - 2 + 3 - 4 + 5. - 100 + 101? (simple calculation)

1^2-2^2+3^2-4^2+...+99^2-100^2+101^2
=(1 + 2) (1-2) + (3-4) (3 + 4) +... + (99 + 100) (99-100) + 101 ^ 2 [square difference formula: A ^ 2-B ^ 2 = (a + b) (a-b)]
=(- 1) [3 + 7 + 11 +... + 199] + 101 ^ 2 (put forward - 1)
=(- 1) * [(3 + 199) * 50] / 2 + 101 ^ 2 (3 + 7 + 11 +... + 199 is an arithmetic sequence with the first term A1 as 3 and the tolerance as 4. There are 50 items in total from a 50 = 199. According to the sum formula of arithmetic sequence: S = (a1 + an) * n / 2 (n is the number of items)]
=-5050+10201
=5151

What is the derivative of y = | x × x-3x-4 | and how to find the derivative with absolute value formula?

To find out by sections
1. When X4:
Y = x × x-3x-4, so y '= 2x-3
2. When 4 > x > - 1:
Y = - x × x + 3x + 4, so y '= - 2x + 3
3. When x = - 1 and x = 4, the left derivative is not equal to the right derivative and the function is not differentiable

Simple operation of 56 × 1.25 decimal point

56x1.25
=7x8x1.25
=7x(8x1.25)
=7x10
=70