Cho hình chóp S.ABCD có đáy ABCD là hình vuông cạnh a. Cạnh bên SA vuông góc với mặt phẳng đáy, khối chóp S.ABCD có thể tích bằng a 3 2 3 . Gọi α là góc giữa hai mặt phẳng (SAD) và (SBD). Tính cos α.

A.  cos α = 3 5

B.  cos α = 6 3

C.  cos α = 2 2 5

D.  cos α = 10 5  

Cho hình lăng trụ tam giác ABC.A’B’C’, gọi M là trung điểm cạnh bên BB'. Đặt C A → = a → ,   C B → = b → ,   C C ' → = c → . Khẳng định nào sau đây là đúng ?

A.  A M → = − a → + b → + 1 2 c →

B.  A M → = a → − 1 2 b → + c →

C.  A M → = − 1 2 a → + b → + c →

D.  A M → = a → + 1 2 b → − c →  

Cho hình chóp tứ giác đều có cạnh đáy bằng a và chiều cao bằng a 3 2 . Tính số đo của góc giữa mặt bên và mặt đáy

A.  45 °

B.  75 °

C.  30 °

D.  60 °  

Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions from 36 to 42.

On March 15, Dunes View Middle School held a contest for school bands. Student bands tried out for the opportunity to perform at the school picnic, which will be held at the end of June. The winner of the contest was the band called Four Square. "We're very proud that we won the contest and are excited to perform at the picnic," says Peter Zandt, who plays the guitar in the band. "And since we hope to perform someday at other local places, like restaurants and parks, this will be a great first step."

The contest was the creation of music teacher Mr. Lopez and drama teacher Ms. Cho. The two thought of the idea while discussing recent years' school picnics. "The picnic is one of the biggest events of the year, but it has become a bit formulaic ," said Ms. Cho. "The activities are the same every year. We thought that a performance by a student band would make the school picnic more interesting and fun." Mr. Lopez, Ms. Cho, and three other teachers judged the contest, which took place in the gym. Eight student bands signed up to audition. The bands varied in their musical forms: there were several rock bands, a folk band, and even a jazz band. "I'm disappointed that my band didn't win, but I think the judges made the right choice," says student Marisol Varga, a member of the folk trio called The Bell Girls. "Four Square is really excellent."

To see if the bands could present a wide range of musical skills, the teachers asked them each to prepare two songs: one song with original words, and another in which students played instrumental music only. The judges finally chose the band Four Square as the winner of the contest. Four Square is a rock band with an unusual twist: it includes a violin player! The members of Four Square write their own songs and practice three times a week after school. Students and teachers agreed that the band competition was a big success. All are looking forward to the school picnic in June.

The word formulaic is closest in meaning to  .

A. expensive 

B. uncertain 

C. long

D. dull