Find the maximum value of the function f (x) equal to minus 4x ^ 2 of x plus 3x minus 9 (x is greater than 0), and the value of X at this time

Find the maximum value of the function f (x) equal to minus 4x ^ 2 of x plus 3x minus 9 (x is greater than 0), and the value of X at this time

F (x) = [- X & # 178; + 3x-9] / (x) = - [x-3 + (9 / x)], because x > 0, then: x + (9 / x) ≥ 6 [if and only if x = 9 / x, i.e. x = 3, take the equal sign], so f (x) ≤ - [6-3] = - 3, then when x = 3, the maximum value of F (x) is - 3
If the problem you provide is correct, then the problem is unsolvable, f (x) = (- 4x ^ 2) / x + 3x-9 = - 4x + 3x-9 = - X-9
Because x is greater than 0, f (x) is the largest when x infinitely approaches 0
Can you make the original title more standard? Completely use the column, not the Chinese characters
f(x)=(-4x^2+3x-9)/x=-4x+3-9/x
Derivation
f'(x）=-4+9/x^2
Let f '(x) = 0
f'(x）=-4+9/x^2=0
Then - 4x ^ 2 + 9 = 0
Because x is greater than 0
x=3/2=1.5
f（3/2）=-9
If equation 3x plus 2 equals 2x plus 1 and equation 4x plus 9 equals 2x plus 1 plus 2K, what is k equal to?
3x+2=2x+1
x=-1
Substitute x = - 1 into 4x + 9 = 2x + 1 + 2K to get 5 = 2k-1
K=3
When a is equal to____ The solution of the equation a (3x-1) = 4x = A-2 is 3
When a is equal to_ 10/7_ The solution of the equation a (3x-1) = 4x + A-2 is 3
a(3x-1)=4x+a-2
3ax-a=4x+a-2
9a-a=12+a-2
8a=a+10
The solution is a = 10 / 7
(1) Finding inequalities 4x-1 / 2 > 3x-1 and 5 (X-2) + 3
4x-1/2>3x-1
Move to: x > - 1 / 2
5(x-2)+3
If the solution set of inequality a ≤ 3 / 4x & # 178; - 3x + 4 ≤ B on X is exactly [a, b], then the value of a + B is——
The answer is 4, but what I get is a = 1, B = 3. The answer is a = 0, B = 4
3／4x²-3x＋4=3／4(x-2)²＋1
On the inequality of x a ≤ 3 / 4x & # 178; - 3x + 4 ≤ B, the solution set is exactly [a, b], then
a≤b
When x = 2, there is a minimum value of 1,
a≤1
When a = 1, B = 3, the solution set of inequality a ≤ 3 / 4x & # 178; - 3x + 4 ≤ B is not [1,3]
So a
Solution inequality: (3x & sup2; + 4x + 7) / (X & sup2; - 3x + 4) < 1
Because x ^ 2-3x + 4 = (x-3 / 2) ^ 2 + 7 / 4 > 0
Therefore, the inequality is as follows:
3x^2+4x+7
Denominator cannot be 0. X is not equal to 0
Then transfer the term, simplify the factorization, draw the number axis, and mark out the answer when several are zero, an interval and an interval test
I can't count.. Only algorithms,,,, can be provided
Because X & sup2; - 3x + 4 > 0
So 3x & sup2; + 4x + 7
Solution inequality: (X & sup2; - 4x + 1) / (3x & sup2; - 7x + 2) ≥ 1
（x^2-4x+1）/（3x^2-7x+2）≥1
x^2-4x+1≥3x^2-7x+2
0≥2x^2-3x+1
0≥(2x-1)(x-1)
1≥x≥1/2
（3x²-7x+2)=(x-2)(3x-1)
Order (X-2) (3x-1)
How to calculate x + 1 / 3x = 3 / 4x + 840
x+1/3x=3/4x+840
4x/3 -3x/4=840
7x/12=840
x=840×12/7=1440
1、4x-1/2(x+5)=5/2 2、2/3x÷0.4×4/5=16 3、9x-12/25÷0.12=167
1、 4x-1/2(x+5)=5/28x-x-5＝57x＝10；x＝10/72、 2/3x÷0.4×4/5=16 2/3x*5/2*4/5＝164/3x＝16； x＝16*3/4＝123、 9x-12/25÷0.12=1679x-12/25*100/12＝1679x-4＝167； x＝171/9＝19
If the point P (2,3) is on the image of a linear function y = 3x-b, then the solution set of inequality 3x-b > 0 is
The point P (2,3) is on the image of linear function y = 3x-b
3=6-b
B=3
therefore
3x-b
=3x-3＞0
x＞1
Substituting point P into the function equation, we get b = 3, and then we solve the inequality to get x > 3
If 3 = 3x2-b, then 3x-3 > 0, then x > 1, that is, X ∈ (1, + ∞)