Equations with unknowns are not always equations

That's right
An equation is an equation with unknowns
For example, 3x + 2 is not an equation

When Xiao Li solves the equation 5a-x = 13 (x is an unknown number), he mistakenly regards - x as + X, and obtains that the solution of the equation is x = - 2, then the solution of the original equation is ()
A. x=0B. x=1C. x=2D. x=3

The original equation is 15-x = 13, the solution is x = 2, so C

To determine the sign of the product, just count the number of negative numbers?

For the result number of calculation, positive or negative depends on the number of negative numbers in the product operation. If the number of negative numbers is odd, the result is negative; if the number of negative numbers is even, the result is positive

How to calculate log2 as bottom 3

Does B & # 178; - 4ac = 0 have two real roots

Yes. It can be said that there are two equal real roots

How to divide the two sides of the inequality? How can the sign change
It's 1 divided by inequality. Wrong number

We're going to talk about symbols
a>b
If a > 0 > b
Obviously, 1 / a > 0 > 1 / b
If a > b > 0
Then 0b
Then 1 / A

How do Mo characters form words? It's the first tone
Attention, it's the first sound of Ma! More than two groups are needed

What's the difference
[interpretation] [rubbing] gently press and move with your hand: rub your hair and your clothes

The method of finding the expression of the symmetrical line of a straight line about a straight line
For example:
Find the expression of symmetric line of y = 2x + 3 with respect to y = x + 1
Substituting X in y = 2x + 3 into Y-1 and Y into x + 1, that is, x + 1 = 2 (Y-1) + 3, the symmetric line is y = 1 / 2x
My question is: does it apply to all such problems?

But this method can not be applied to all cases, only when the slope of the axis of symmetry is ± 1. Wrong example: for example, find the symmetric line of y = √ 3x with respect to y = (√ 3 / 3) x: according to this method, substitute X in y = √ 3x into √ 3Y, y into (√ 3 / 3) x, and get (√ 3 / 3) x = 3Y, y = (√ 3 / 9) X

Ask 200 written arithmetic questions for grade two of primary school
I don't know the difference between written arithmetic and oral arithmetic. Is it more difficult?

The difference between oral arithmetic and written arithmetic:
Oral calculation: it is relatively simple and has calculation skills. You can quickly calculate the number without writing
Written calculation: some need skills, some do not have skills, you need to calculate the number of written calculation
Written calculation:
22+35-12 35+46-7 12-6+21 65-42+13
36-25+13 27-8+3 20+3-2 29+3-20

Discuss the number of real roots of equation: e ^ x = ax ^ 2. A > 0
Please use the advanced number method to solve this problem. This is my homework of mathematical analysis,

Let f (x) = e ^ x, G (x) = ax ^ 2, H (x) = f (x) - G (x)
It is easy to get H (- ∞) < 0, H (0) > 0, so there must be a point x = x0, so that
H (XO) = O, i.e
F (XO) = e ^ XO = g (XO) = axo ^ 2
E ^ x = ax ^ 2 has a real root on (- ∞, 0)
Because e ^ x = ax ^ 2, the right side of the equation is rewritten to the left side. When x > 0, there is
X = LNA + 2lnx (exponentially equal)
Let u (x) = x-lna-2lnx have
u'(x)=1-2/x
Let u '(x1) = O give X1 = 2 and
When x ＜ x1, u '(x) ＜ 0; when x ＞ x1, u' (x) ＞ 0
Therefore, in order for the equation to have roots, H (x1) ≤ 0 is necessary
A ≥ e ^ 2 / 4 and
u(+∞)＞0
It is easy to prove that x is greater than LNX by using the law of lobita
U (+ ∞) > 0 holds
in summary:
When 0 < a < e ^ 2 / 4, the equation has only one real root;
When a = e ^ 2 / 4, there are two real roots;
When a > e ^ 2 / 4, there are three real roots

Equations with unknowns are not always equations