(1)C

(2)A

(3)G

(4)D

(5)B

(6)F

(7)E

a, Thay k=0 vào phương trình, ta có:

\(4x^2-25=0\)

\(4x^2=25\Rightarrow x=\sqrt{\dfrac{25}{4}}=\dfrac{5}{2}.\)

Vậy nghiệm của PT là \(\dfrac{5}{2}\)khi k=0.

b, Thay k=-3 vào phương trình, ta có:

\(4x^2-25+9-12x=0\)

\(4x^2-12x=16\)

\(x^2-3x=4\)

\(x^2-3x-4=0\)

\(x^2-4x+\left(x-4\right)=0\)

\(\left(x-4\right)\left(x+1\right)=0\)

\(\Rightarrow x-4=0\) hoặc \(x+1=0\)

\(\Rightarrow x=4\) hoặc \(x=-1\)

Vậy phương trình có hai nghiệm là 4 và -1 khi k=-3.

c, Cho : \(16-25+k^2-8k=0\)

\(k^2-8k-9=0\)

\(k^2-9k+\left(k-9\right)=0\)

\(\left(k-9\right)\left(k+1\right)=0\)

\(\Rightarrow k-9=0\) hoặc \(k+1=0\)

\(\Rightarrow k=9\) hoặc \(k=-1\)

Vậy các giá trị của k là 9 và -1 để pt nhận x=-2 làm nghiệm.

ko có số nào cả vì ko có số lớn nhất

-Theo mình nghĩ thì ta có công thức tính vận tốc trung bình là:

\(\dfrac{S}{t1+t2}\)(trong đó S là cả quãng đường; t1, t2 lần lượt là thời gian đi trên mỗi nửa quãng đường)

Sai thì cho sorry nhé ^^

1.They last talked to each other two months ago. ---> They haven't talked to each other for two months.

2.The last time she saw her elder sister was in 1999. --->She hasn't seen her elder sister since 1999.

3.She hasn't written to me for years.---> It's years since she wrote to me.

4.Robert and Catherine have been married for ten years.--->It's ten years Robert and Catherine married.

5.It's two weeks since they deaned their room.----->They haven't cleaned their room for two weeks.

6.It's over six months since John had his hair cut.---->John has had his hair cut for over six months.

7.how long is it since he wrote to you?--->When was the last time he wrote to you?

8.I last had my hair cut when I left her.--->I haven't had a new hair cut since I left her.

9.The last time she kissed me was 5 months ago.--->She hasn't kissed me for 5 months.

10.It is a long time since we last met.--->We haven't met for a long time.

11.I haven't seen him for 8 days.-->The last time I saw him was 8 days ago.

12.I haven't taken a bath since Monday.-->It is last Monday since I took a bath.

13.It's 2 years since i had a punture.--->I have had a punture for 2 years.

14.It's 2 months since he earned any money.--->He has earned any money for two months.

Hi Leslie,

I'm very pleased to receive an invitation to your party. Well, I have an extra class at 4 on Saturday, so I can come after 6 pm. Is that alright? If it's possible, can I also come with my classmate, Lily? I'm keen on organising a game for everyone at parties. By the way, can you prepare some board games? Then, we can play together after the party. That'll be fun.

If my idea's OK, email me soon.

Violet.

-tienganh123

\(A=5-4x^2+4x=-4x^2+4x+5=-\left(4x^2-4x+1\right)+6=-\left(2x-1\right)^2+6=6-\left(2x-1\right)^2\)

Ta có : \(\left(2x-1\right)^2\ge0\)

\(\Rightarrow6-\left(2x-1\right)^2\le6\)

\(\Rightarrow\) MaxA=6 \(\Leftrightarrow2x-1=0\)

MaxA=6 \(\Leftrightarrow\)x = 0,5.

Vậy giá trị lớn nhất của biểu thức A là 6 khi x=0,5.