The books on the shelf are old

The books on the shelf are old

The books on the bookshelf are old

There are some books in the bookcase

There are some books in the bookcase

Partial differential problems of implicit functions
Given f (x, y, z) = 0, z = f (x, y)
Please use some partial derivatives of F to express d2z / (DXDY)

The condition of this question also reminds you that it's not easy to make a sign. I'll forgive you. Note: when f calculates the partial derivative of X, Z must be regarded as a constant. The partial derivative of Z to x = (- 1) the partial derivative of F to X / the partial derivative of F to Z. then use the above expression to calculate the partial derivative of Y. note that Z should be regarded as a function of Y! The final result is f'x [f '

Find the derivative function of y = x 2 of COS X!

y'=((x^2)'cosx-x^2(cosx)')/cosx^2
= (2xcosx+x^2sinx)/cosx^2
This is the final answer. It can't be simplified

In 1993, 1992, the numerator subtracts a number, the denominator adds this number, the score is 2 / 3, find this number

Let this number be X
(1992-X)/(1993+X)=2/3
Multiply both sides by 2 (1993 + x)
2(1993+X)=3(1992-X)
2986+2X=5976-3X
2X+3X=5976-2986
5X=2990
X=598
This number is 598

Why is the general solution of the differential equation y '' - 3Y '+ 2Y = 0?
Differential problem

Y = C1 times the x power of E + C2 times the 2x power of e

Given that M & # 178; = n + 2, n & # 178; = m + 2, (m ≠ n), find the value of (1) m + N and (2) M & # 179; - 2Mn + n & # 179;. Please explain in detail,

This paper is n + 2, n \\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\\178; = m +

In a formula with only multiplication and division, we should first calculate multiplication and then division. B. in a formula with only multiplication and division
Right ()
A. Only in the formula of multiplication and division, we should first calculate multiplication and then division
B. In a formula, there are both brackets and brackets. We should first calculate the one in the brackets and then calculate the one in the brackets
C. Each recording pen is 105 yuan, and Mr. Wang has 500 yuan. He can only buy four at most

C. If you get a, you should follow the order from left to right. If you get B, you should first get parentheses, then brackets, not brackets

In the space coordinate system, we know that the three vertices of the right triangle ABC are a (- 3, - 2,1), B (- 1, - 1, - 1), C (- 5, x, 0), then the value of X is______ ．

∵ a (- 3, - 2,1), B (- 1, - 1, - 1), C (- 5, x, 0), ∵ AB = (2,1, - 2), BC = (- 4, x + 1,1), AC = (- 2, x + 2, - 1) can be divided into three cases: ① A is right angle, ab · AC = 0, ∵ 4 + X + 2 + 2 = 0, ∵ x = 0; ② B is right angle, ab · BC = 0, ∵ - 8 + X + 1-2 = 0, ∵ x = 9; ③ C is right angle, AC · BC = 0, ∵ 8 + (x + 1) (x + 2) - 1 = 0, X2 + 3x + 9 = 0. To sum up, the value of X is 0 Or 9, so the answer is: 0 or 9

Known 0

We should use the method of constructing angle
Cos β = cos [α - (α - β)] is to treat β as the angle of α minus (α - β). The condition is enough. Just find out the values of sin α and sin (α - β), and then use the formula of the difference between the two angles!