Given the function f (x) = {log3x, x > 0; 2 ^ x, X ≤ 0, then f (f (1 / 9))

Given the function f (x) = {log3x, x > 0; 2 ^ x, X ≤ 0, then f (f (1 / 9))

f(1/9)=log3(1/9)=-2
f(f(1/9))=f(-2)=2^(-2)=1/4

(1) In the complex set, any real Coefficient Quadratic Equation with one variable has solutions. (2) in the complex set, any real Coefficient Quadratic Equation with one variable has two conjugate complex roots. Are these two propositions correct? When the imaginary part is 0, is it conjugate complex? For example, if the solution of an equation is two real numbers a, B, X1 = a + 0I, X2 = B + 0I, is it conjugate?

When AB, it is not conjugate
Only when a = B, x 1 = a + 0I, x 2 = B + 0I, is conjugate

There are 150 kg pears in the fruit shop. The weight of peach is three fifths that of pear and two seventh that of apple. How many kg are apples?

First, the weight of peach is 150x3 / 5 = 90kg, so the weight of apple is 90x7 / 2 = 315kg

Angle: it is known that ∠ 1 and ∠ 2 are adjacent complementary angles, and ∠ 1 and ∠ 3 are opposite vertex angles, then ∠ 2 plus ∠ 3 equals ()

Of course, it's 180 degrees. If ∠ 1 and ∠ 3 are opposite to each other, then ∠ 1 and ∠ 3 are equal
Since ∠ 1 and ∠ 2 are complementary angles, so ∠ 1 + 2 is equal to 180 degrees, then ∠ 2 plus ∠ 3 is equal to 180 degrees

If the vector expression of a sine quantity u = 50 ∠ 30 °, then its sine function expression is ()
A、u=50sin（wt+30°） B、u=50√2sin（wt+30°） C、u=50sin（wt-30°） D、u=50√2sin（wt-30°）

U = 50 √ 2Sin (WT + 30 °) select B

A group of students set out from school for an outing and walked at the speed of 4 km / h. after 1.5 o'clock, a teacher rode to see them
A group of students set out from school for an outing and walked at the speed of 4 km / h. after 1.5 o'clock, a teacher rode a motorcycle to catch up with the students from the same road at 0.25 o'clock to find the speed of the motorcycle

Let the motorcycle speed be x km
0.25X=4×（1.5+0.25）
0.25X=7
X=28

The fourth power of M - the fourth power of 16N
Factorization

(M + 2n) (m-2n) (the second power of M + the second power of 4N)
The formula used is the square difference formula A & # 178; - B & # 178; = (a + b) × (a-b)

How to use the right hand rule of vector cross product?
If it is perpendicular to the plane of the original vector, then it has no direction to talk about?

For example, a = (1,0,0) and B = (0,1,0) represent the positive direction of X and Y axes respectively. Then with the right hand rule, we know that the direction of C = A and B should be the positive direction of Z axis, that is, C = (0,0,1) I don't know

600 teachers and students of Yucai Middle School went out to visit the exhibition of science and Technology Museum. The school is going to rent a car to go there. It is known that a bus carries 20 more people than a van,
If all the teachers and students take minibuses, how many do the schools need to rent? How many do they need to take buses,

The minibus can carry x people and the bus can carry x + 20 people
10x = 6 (x + 20) gives x = 30
Minibuses carry 30 passengers and buses carry 50 passengers
Dividing the number of passengers by the number of passengers, it takes 12 to take a big bus and 20 to make bread

How to prove that the function y = cos & # 178; (1 / x) has no left and right limit at x = 0?

First of all, limit cos (x) does not exist when x is compact to infinity, because the function oscillates
Let z = 1 / x, then the problem becomes to prove that y = cos ^ 2 (z) does not exist when Z tends to infinity
(y = cos ^ 2 (z) = (1 + cos (2Z)) / 2, where cos (2Z) limit does not exist)