What are the three categories of natural numbers

Rational number, irrational number, real number

1. How many kinds of electricity are there? What are they? What are their symbols?

AC, AC, DC
It can also be divided into strong electricity (above lighting) and weak electricity (signal electricity such as TV and telephone)

Know how to divide the group distance into several groups of mathematics
A sample contains 10 data, 52.51 49 50 51 48 53 If the group distance is 1.5, it should be divided into two groups__ group

It should be divided into three groups
Subtract the minimum number from the maximum number, divide it by the group distance, and then round it up
For example, 63-49 = 4 4 / 1.5 = 2.666 ≈ 3, so they are divided into three groups

Log with 3 as the base, log with 10 = a, log with 6 as the base, log with 25 = B, log with 4 as the base, log with 45 =?

log3(10)=a,log3(2)+log3(5)=a,log3(25)/log3(6)=b,[2log3(5)]/[log3(2)+1]=b,log3(2)=(a-b)/(b+1),log3(5)=[b(a+1)]/(b+1).log4(45)=[log3(5)+2]/[2log3(2)]=[b(a+1)+2(b+1)]/[2(a-b)]=[ba+3b+2]/[2(a-b)].

If the quadratic equation of one variable: ax ^ 2 + (A-2) x + 1 = 0, one root X1 is in (- 1,1) and the other root (1,2), find the range of a?

f(-1)=a-a+2+1=3
f(1)=a+a-2+1=2a-1
f(2)=4a+2a-4+1=6a-3=3(2a-1)
If a root X1 is in (- 1,1), then f (- 1) f (1)

It is known that the abscissa of the intersection of parabola and x-axis is - 1 and 3, and its vertex is on the straight line y = x + 1. The analytic expression of quadratic function is obtained

Let y = a (x + 1) (x-3)
The result is y = ax ^ 2-2ax-3a
Then the axis of symmetry x = 1, that is, the abscissa of the vertex is y = x + 1
So y = 2
Finally, we take the vertex into the above formula and get a, then we can get the quadratic function

1.2（x+3.7）=14.4

8.3

About x ^ 2 + 2x + 1 / x ^ 2 + X in three minutes

x^2+2x+1/x^2+x
=（x+1）²/x(x+1)
=(x+1)/x
If you don't understand this question, you can ask,

How to solve the quadratic equation x ^ 2 + 2x-8 = 0 with formula method,

△=2²-4×1×(-8)
=4+32
=36
So, X1 = (- 2 + √ 36) / (2 × 1)
=(-2+6)/2
=2
x2=(-2-√36)/(2×1)
=(-2-6)/2
=-4

What are the three categories of natural numbers