\(9-9x^2+2x-\dfrac{2}{9}\\ =-\left(9x^2-2x+\dfrac{1}{9}-\dfrac{80}{9}\right)\\ =-\left(3x+\dfrac{1}{3}\right)^2+\dfrac{80}{9}\le\dfrac{80}{9}\)

Dấu "=" xảy ra khi \(-\left(3x+\dfrac{1}{3}\right)^2=0\)

\(\Leftrightarrow3x+\dfrac{1}{3}=0\\ \Leftrightarrow3x=-\dfrac{1}{3}\\ \Leftrightarrow x=-\dfrac{1}{9}\)

Vậy \(Max=\dfrac{80}{9}\Leftrightarrow x=-\dfrac{1}{9}\)

9 - 9x² + 2x - \(\dfrac{2}{9}\)
=\(\dfrac{80}{9}\)-[(3x)²-2x+(\(\dfrac{1}{3}\))²]
=\(\dfrac{80}{9}\)-(3x-\(\dfrac{1}{3}\))²
Vì (3x-\(\dfrac{1}{3}\))²≥0 ⇒-(3x-\(\dfrac{1}{3}\))²≤0⇒\(\dfrac{80}{9}\)-(3x-\(\dfrac{1}{3}\))²≤\(\dfrac{80}{9}\)
Trường hợp dấu bằng xảy ra khi: (3x-\(\dfrac{1}{3}\))²=0⇒3x-\(\dfrac{1}{3}\)=0⇒3x=\(\dfrac{1}{3}\)⇒x=\(\dfrac{1}{9}\)
Vậy GTLN của biểu thức là \(\dfrac{80}{9}\) khi x=\(\dfrac{1}{9}\)

 

10.213

11. 2 giờ 55 phút

12. 4 ngày 21 giờ

13.

a: 6,008

b: 4500

c: 5,628

d: 4,009

14.

a,8579 cm2

b,32,04 m2

c,187200m2

d,5,017 tấn

14:

a: \(85.79km^2=857900000000cm^2\)

b: \(32m^24dm^2=32.04m^2\)

c: \(1872dm^2=18.72m^2\)

d: 5 tấn 17kg=5,017 tấn

13:

a: \(6dm^38cm^3=6.008dm^3\)

b: \(4.5m^3=4500dm^3\)

c: \(5628dm^3=5.628m^3\)

d: \(4m^39dm^3=4.009m^3\)

12: =108h:3+80h

=36h+80h=116h

10:

3h18p+7h21p:3

=198p:441p:3

=198p+147p=345p

=(4x0.25)x(2x0.5)

=1x1=1

a) (2/5 x 25/29) + (3/5 x 25/29)
= (50/145) + (75/145)
= 125/145

b) (5/2 x 3/7) - (3/14 : 6/7)
= 15/14 - (3/14 x 7/6)
= 15/14 - 1/2
= (30/28) - (14/28)
= 16/28
= 4/7

c) (15/4 : 5/12) - (6/5 : 11/15)
= (15/4 x 12/5) - (6/5 x 15/11)
= 180/20 - 90/55
= 9 - 18/11
= (99/11) - (18/11)
= 81/11
= 7 4/11

a) (2/3) + (20/21 x 3/2 x 7/5)
= 2/3 + (60/210)
= 2/3 + 2/7
= (14/21) + (6/21)
= 20/21

b) (5/17 x 21/32 x 47/24 x 0)
= 0

c) (11/3 x 26/7) - (26/7 x 8/3)
= (286/21) - (208/21)
= 78/21
= 3 9/21
= 3 3/7

a) (25/8) : x = 5/16
=> (25/8) x (16/5) = x
=> 4 = x

b) x + (7/15) = 6/15
=> x = (6/15) - (7/15)
=> x = -1/15

c) x : (28/49) = 7/12
=> x x (49/28) = 7/12
=> x = (7/12) x (28/49)
=> x = 1/2

a) 6 x x = (5/8) : (3/4)
=> 6x = (5/8) x (4/3)
=> 6x = 20/24
=> 6x = 5/6
=> x = (5/6) / 6
=> x = 5/36

câu,b,không,đủ,thông,tin,nhan,bạn.

\(\dfrac{1}{2}\times\dfrac{1}{3}+\dfrac{3}{4}\)

\(=\dfrac{1}{6}+\dfrac{3}{4}\)

\(=\dfrac{2}{12}+\dfrac{9}{12}\)

\(=\dfrac{11}{12}\)

____________________________

\(\dfrac{3}{7}-\dfrac{2}{7}:\dfrac{2}{3}\)

\(=\dfrac{3}{7}-\dfrac{2}{7}\times\dfrac{3}{2}\)

\(=\dfrac{3}{7}-\dfrac{3}{7}\)

\(=0\)

Chúc bạn học tốt

1/2 x 1/3 + 3/4 = 1/6 + 3/4 = 4/24 + 18/24 = 22/24 = 11/12
3/7 - 2/7 : 2/3 = 3/7 - 2/7 x 3/2 = 3/7 - 3/7 = 0

1​×31​+43​

=16+34=61​+43​

=212+912=122​+129​

=1112=1211​

____________________________

37−27:2373​−72​:32​

=37−27×32=73​−72​×23​

=37−37=73​−73​

$=0$

Ta có: \(\left(3\dfrac{3}{4}+\dfrac{4}{7}\cdot\dfrac{7}{16}\right):\dfrac{1}{2}\)

\(=\left(\dfrac{15}{4}+\dfrac{1}{4}\right)\cdot2\)

\(=4\cdot2=8\)

Ta có:\(\left(3\dfrac{3}{4}+\dfrac{4}{7}.\dfrac{7}{16}\right):\dfrac{1}{2}\)

       \(=\left(\dfrac{15}{4}+\dfrac{1}{4}\right).2\)

       \(=\dfrac{16}{4}.2\)

       \(=8\)

= 4 : 1/2 = 4 nhân 2/1  = 8

đáp án = 8

= 4 : 1/2 = 4 nhân 2/1  = 8

đáp án = 8