1 A

2 B

3 A

4 A

5 A

6 C

7 D

8 B

89x(19-16+3)=89x6=534

C giai giúp bé  rồi nhé

vâng ạ , em cảm ơn Phạm Thu Trang ạ <3

giải cái gì bạn

c c a b b a d b a c

Bài 1: 

a) Ta có: \(A=x^2-2x+7\)

\(=x^2-2x+1+6\)

\(=\left(x-1\right)^2+6\ge6\forall x\)

Dấu '=' xảy ra khi x=1

b) Ta có: \(B=5x^2-20x\)

\(=5\left(x^2-4x+4-4\right)\)

\(=5\left(x-2\right)^2-20\ge-20\forall x\)

Dấu '=' xảy ra khi x=2

d) Ta có: \(D=4x^2+4x+11\)

\(=4x^2+4x+1+10\)

\(=\left(2x+1\right)^2+10\ge10\forall x\)

Dấu '=' xảy ra khi \(x=-\dfrac{1}{2}\)

Bài 2: 

a) Ta có: \(A=-x^2+10x-2\)

\(=-\left(x^2-10x+2\right)\)

\(=-\left(x^2-10x+25-23\right)\)

\(=-\left(x-5\right)^2+23\le23\forall x\)

Dấu '=' xảy ra khi x=5

b) Ta có: \(B=-2x^2+2x+3\)

\(=-2\left(x^2-x-\dfrac{3}{2}\right)\)
\(=-2\left(x^2-x+\dfrac{1}{4}-\dfrac{7}{4}\right)\)

\(=-2\left(x-\dfrac{1}{2}\right)^2+\dfrac{7}{2}\le\dfrac{7}{2}\forall x\)

Dấu '=' xảy ra khi \(x=\dfrac{1}{2}\)

1 that => which

2 he => who

3 hardly => hard

4 quick => quickly

5 turning off  => turning on

6 to => and

7 For => therefore

8 therefore => so

9 to have => having

10 to swim => swimming

11 will go => go

12 don't => won't

13 was => is

14 for => since

15 didn't => haven't

\(v_o=36km/h=10m/s\\ v=54km/h=15m/s\\ s=625m\)

a) Gia tốc của xe là:

\(v^2-v_o^2=2as\rightarrow a=\dfrac{v^2-v_o^2}{2s}=\dfrac{15^2-10^2}{2.625}=0,1\left(m/s\right)\)

b) Thời gian tăng tốc:

\(a=\dfrac{v-v_o}{t}\rightarrow t=\dfrac{v-v_o}{a}=\dfrac{15-10}{0,1}=50\left(s\right)\)

13 B

14 B

15 C