It is known that the function f (x) = 13x3-12x2 + CX + D obtains the extremum at x = 2. (1) find the value of C; (2) when x < 0, f (x) < 16d2 + 2D holds, and find the value range of D

It is known that the function f (x) = 13x3-12x2 + CX + D obtains the extremum at x = 2. (1) find the value of C; (2) when x < 0, f (x) < 16d2 + 2D holds, and find the value range of D

(1) ∵ f (x) gets the extremum at x = 2, ∵ f ′ (2) = 4-2 + C = 0, ∵ C = - 2. ∵ f (x) = 13x3-12x2-2x + D, (2) ∵ f ′ (x) = x2-x-2 = (X-2) (x + 1), ∵ when x ∈ (- ∞, - 1], f ′ (x) > 0, the function monotonically increases; when x ∈ (- 1,2], f ′ (x) < 0, the function monotonically decreases When 76 + D, ∵ x ＜ 0, f (x) ＜ 16d2 + 2D is constant, ∪ 76 + D ＜ 16d2 + 2D, i.e. (D + 7) (D-1) ＞ 0, ∪ D ＜ - 7 or D ＞ 1, i.e. the value range of D is (- ∞, - 7) ∪ (1, + ∞)

The known function f (x) = (x-a) & sup2; (X-B) (a, B ∈ R, a)

F '(x) = 2 (x-a) (X-B) + (x-a) ^ 2 = (x-a) (3x-2a-b), so the extreme points are a and (2a + b) / 3, so the zero point must be B (the other zero point is a, which does not satisfy the condition). That is, X3 = B, X1 = a, X2 = (2a + b) / 3. In this case, take X4 = (a + 2b) / 3, and arrange it in the order of x1, X2, x4, X3. In fact, X2 is a trisection point of a and B, so the other trisection point is X4

(1 / 2) plus 1 and 3 / 7 minus 5 / 6
Comprehensive formula
Wrong writing should be: (1 / 2 + 2 / 5) × 1 and 3 / 7-5 / 6

I changed it
Original formula = (5 / 10 + 4 / 10) × 10 / 7 minus 5 / 6
=9 out of 10 times 10 out of 7 minus 5 out of 6
=9 / 7-5 / 6
=54 out of 42 - 35 out of 42
=19 out of 42

A cuboid fish pond is 8 meters long, 4.5 meters wide and 2 meters deep. What is the volume of the pond?

8 × 4.5 × 2 = 72 cubic meters. A: the volume of this fish pond is 72 cubic meters

What is 15 times 1 / 20 divided by 7 / 8

15*1/20*7/8=6/7

Divide 100 into the sum of two natural numbers, one is a multiple of 7, the other is a multiple of 11. These two natural numbers are______ And______ ．

Because 100 = 7 × 8 + 11 × 4, the two natural numbers are 56 and 44, so the answer is 56, 44

Calculation method 120-36 * 4 ＼ 18 + 35

Of course, it's multiplication and division before addition and subtraction
120-36×4÷18+35
=120-144÷18+35
=120-8+35
=112+35
=147

If a & # 178; + B & # 178; = 2Ab, how to prove a = B

∵a²+b²=2ab
The result is: A & # 178; + B & # 178; - 2Ab = 0
The left factorization is: (a-b) &# = 0
∴a-b=0
That is, a = B

Put the nine numbers 0, 1, 2, 3, 4, 5, 6, 7 and 8 into the nine palace grid in the figure below. Add the three numbers in each row, column and diagonal to get eight sums. The sum of the eight sums is the largest______ ．

If the middle point of the nine palace grid is used for four times, fill in 8; if the four corners are used for three times, fill in 7, 6, 5, 4; if the four sides are used for two times, fill in 3, 2, 1, 0; if the maximum sum is 8 × 4 + (7 + 6 + 5 + 4) × 3 + (3 + 2 + 1 + 0) × 2 = 110

Help me solve the quadratic equation {0.6x-0.4y = 1.1}? 0.2x-0.4y = 2.3
{4（x-y-1)=3(1-y)-2
2 / x + 3 / y = 2, then help me calculate this.

0.6x-0.4y=1.1
0.2x-0.4y=2.3
4 x = - 1. 2 x = - 3
Substituting x = - 3 into an equation, y = - 29 / 4