A = {0;1;2;3;4;5;6;7;8;9;10;11}

Sai thì nhắc mik nhé!

(4x - 1) - (4x + 1)(x - 2) = 12

=> 4x - 1 - 4x² - 7x - 2 = 12

=> (4x - 7x) + (- 1 - 2) - 4x² = 12

=> -3x - 3 - 4x² = 12

=> -3x - 4x² = 15

=> không tồn tại x 

b. (2x - 3)(2x + 1) - (2x - 2)(2x - 2) = 15

=> 2x(2x + 1) - 3(2x + 1) - 2x(2x - 2) + 2(2x - 2) = 15

=> 4x² + 2x - 6x - 3 - 4x² + 4x - 4x - 4 = 15

=> (4x² - 4x²) + (2x - 6x + 4x - 4x) + (-3 - 4) = 15

=> -4x - 7 = 15

=> -4x = 22

=> x = \(-\frac{11}{2}\)

a, \(\left(4x-1\right)-\left(4x+1\right)\left(x-2\right)=12\)

\(\Leftrightarrow4x-1-4x^2+8x-x+2=12\)

\(\Leftrightarrow11x+1-4x^2=12\)

\(\Leftrightarrow11x-11-4x^2=0\)( vô nghiệm )

b, \(\left(2x-3\right)\left(2x+1\right)-\left(2x-2\right)^2=15\)

\(\Leftrightarrow4x^2+2x-6x-3-4x^2+8x-4=15\)

\(\Leftrightarrow4x-7=15\Leftrightarrow4x=22\Leftrightarrow x=\frac{11}{2}\)

a) \(\left(4x-1\right)-\left(4x+1\right)\left(x-2\right)=12\)

\(\Leftrightarrow4x-1-\left(4x^2-7x-2\right)=12\)

\(\Leftrightarrow4x-1-4x^2+7x+2=12\)

\(\Leftrightarrow4x^2-11x+11=0\)( Pt vô nghiệm )

b) \(\left(2x-3\right)\left(2x+1\right)-\left(2x-2\right)^2=15\)

\(\Leftrightarrow\left(4x^2-4x-3\right)-\left(4x^2-8x+4\right)=15\)

\(\Leftrightarrow4x=22\)

\(\Leftrightarrow x=\frac{11}{2}\)

Ta có C = (x² + 2xy + y²) + (y² - 6x + 9) + 6 

= (x + y)² + (y - 3)² + 6 \(\ge6>0\)(đpcm)

C = x² + 2xy + y² + y² - 6y + 15 

C = ( x² + 2xy + y² ) + ( y² - 6y + 9 ) + 6

C = ( x + y )² + ( y - 3 )² + 6 ≥ 6 > 0 ∀ x ( đpcm )

D = x² + y² + 6x + 10y + 30

D = ( x² + 6x + 9 ) + ( y² + 10y + 25 ) - 4

D = ( x + 3 )² + ( y + 5 )² - 4 ≥ -4 ( xem lại đề nhớ )

\(Tacó\):   \(C=x^2+2xy+y^2+y^2-6y+15\)

\(=\left(x^2+2xy+y^2\right)+\left(y^2-6y+9\right)+6\)

\(=\left(x+y\right)^2+\left(y-3\right)^2+6\)

\(Mà\)\(\left(x+y\right)^2\ge0\)với mọi x,y

             \(\left(y-3\right)^2\ge0\)với mọi y

\(\Rightarrow\left(x+y\right)^2+\left(y-3\right)^2+6>0\)

\(Hay\)\(x^2+2xy+y^2+y^2-6y+15>0\)\

: 

a.\(\left(4x-1\right)-\left(4x+1\right).\left(x-2\right)=12\)

\(\Leftrightarrow4x-1-\left(4x^2-7x-2\right)-12=0\)

\(\Leftrightarrow4x-1-4x^2+7x+2-12=0\)

\(\Leftrightarrow-4x^2+11x-11=0\)

\(\Rightarrow4x^2-11x+11=0\)

\(\Leftrightarrow\left(2x\right)^2-2.2x.\frac{11}{4}+\frac{11^2}{4^2}-\frac{11^2}{4^2}+11=0\)

\(\Leftrightarrow\left(2x-\frac{11}{4}\right)^2+\frac{55}{16}=0\)( VÔ LÝ )

VẬY KHÔNG CÓ GIÁ TRỊ NÀO CỦA x THỎA MÃN PT ĐÃ CHO

b. \(\left(2x-3\right).\left(2x+1\right)-\left(2x-2\right)^2=15\)
\(\Leftrightarrow4x^2-4x-3-4x^2+8x-4-15=0\)

\(\Leftrightarrow4x-22=0\)\

\(\Leftrightarrow x=\frac{11}{2}\)

VẬY PT CÓ NGHIỆM x= 11/2

Giúp mình nha. Bài cuối cùng của đề toán dài 36 bài của mình đó

\(A=\frac{1}{2.2}+\frac{1}{3.3}+\frac{1}{4.4}+...+\frac{1}{100.100}< \frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}\)

Mà \(\frac{1}{1.2}+\frac{1}{2.3}+\frac{1}{3.4}+...+\frac{1}{99.100}=1-\frac{1}{2}+\frac{1}{2}-\frac{1}{3}+\frac{1}{3}-\frac{1}{4}+...+\frac{1}{99}-\frac{1}{100}=1-\frac{1}{100}< 1\)

Nên từ đây => \(A< 1\)     (ĐPCM)

1 The last time she taught English me we was 5 months ago

=>She hasn't..taughr me English for 5 month.......

2 It is a long time since we last met.

=>We haven't.met for a long time.......

3 When did you have it ?

=> How long.have you had it.?.....

4 This is the first time. I had such a delicious meal.

=> I haven't..had a delicous meal before........

5 I haven't taken a bath since Monday 

=> It is .the last time I have taken a bath since Monday......

6 It's 2 years since I had a punture

=> I haven't .had a puniture for 2 years....

7 It's 2 month since he earned any money

=> He has .earned money for 2 months...

8 He last shaved the day before yesterday

=> He hasn't.shaved for 2 days....

9 I last drank champagne at my brother's wedding

=> I haven't .drunk champagne since my brother's wedding........

10 It's  2 years since I was last in Rome 

=> I haven't .been to Rome.for 2 years........

11 I saw Tom last on his weddind day 

=> I haven't ..seen Tom since his wedding day.....

12 I last ate raw fish when was in Japan 

=> I haven't...eaten raw fish since I was in Japan..