Mark the letter A, B, C, or D on your answer sheet to indicate the sentence that is closest in meaning to the sentence(s) in italics.

He needn’t have hurried as the meeting didn’t start until quite a while after the time for which it had been planned.

A. The meeting started rather later than scheduled, so it wasn't necessary for him to hurry

B.  There was no need for him to hurry because he had plenty of time before the scheduled time of the meeting.

C.  He didn’t need to hurry as he already knew that the meeting wouldn’t start as scheduled.

D. He wouldn't have arrived at the meeting on time if he hadn't hurried.

Hỗn hợp E gồm ba peptit mạch hở X, Y, Z (M_X < M_Y < M_Z). Thủy phân hoàn toàn 38,12 gam E bằng dung dịch KOH vừa đủ, cô cạn dung dịch sau phản ứng, thu được 60,68 gam hỗn hợp F gồm hai muối có dạng H₂NC_nH_2nCOOK. Đốt cháy hoàn toàn F cần vừa đủ 1,77 mol O₂. Biết X chiếm 25% tổng số mol hỗn hợp. Phần trăm khối lượng của Y trong E có giá trị gần nhất với giá trị nào sau đây?

A. 55

B. 50

C. 45

D. 60

\(\Leftrightarrow A=\left(\dfrac{x}{x+2}+\dfrac{\left(x-2\right)\left(x^2+2x+4\right)}{\left(x+2\right)\left(x^2-2x+4\right)}.\dfrac{\left(x-2\right)^2}{-\left(x-2\right)\left(x+2\right)}\right):\dfrac{4}{x+2}\)

\(\Leftrightarrow A=\left(\dfrac{x}{x+2}-\dfrac{\left(x-2\right)\left(x+2\right)^2}{\left(x+2\right)\left(x-2\right)^2}.\dfrac{-\left(x-2\right)}{\left(x+2\right)}\right):\dfrac{4}{x+2}\)

\(\Leftrightarrow A=\left(\dfrac{x}{x+2}-1\right):\dfrac{4}{x+2}\)

\(\Leftrightarrow A=\dfrac{2}{x+2}:\dfrac{4}{x+2}\)

\(\Leftrightarrow A=\dfrac{1}{2}\)

a) Xét\(\Delta\) ADB và \(\Delta\)ACE có:

Góc A chung

Góc D = Góc E (=90⁰)

\(\Rightarrow\)\(\Delta\)ADN \(\infty\) \(\Delta\)ACE ( g.g )

b) Xét \(\Delta\)HEB và \(\Delta\)HDC có:

Góc ABD = Góc ACE ( CM ý a)

Góc E = Góc D ( =90⁰)

\(\Rightarrow\)\(\Delta\)HEB\(\infty\) \(\Delta\)HDC ( g.g )

\(\Rightarrow\) \(\dfrac{HE}{HD}=\dfrac{HB}{HC}\) \(\Rightarrow\) HE.HC = HB.HD

c) Xét AFC và IFC có:

Góc C chung

Góc F = Góc I ( = 90⁰ )

^{\(\Rightarrow\Delta AFC\infty\Delta FIC\left(g.g\right)\)}

\(\Rightarrow\dfrac{AF}{IF}=\dfrac{FC}{IC}\Rightarrow\dfrac{AF}{FC}=\dfrac{IF}{IC}\)

a) a<b \(\Rightarrow\) a+c < b+c (1)

c<d\(\Rightarrow\) c+b < d+b (2)

Từ 1 và 2 \(\Rightarrow\)a+c < b+d (dpcm)

b) a<b \(\Rightarrow\) ac < bc ( vì c dương) (1)

c < d\(\Rightarrow\) bc < bd (vì b dương) (2)

Từ 1 và 2 \(\Rightarrow\) ac < bd (đpcm)