Re: [計量] 幾題CAT問題想請教

看板GRE (GRE入學考試)作者osiris5435 (osiris5435)時間16年前 (2009/08/20 22:41)推噓1(1推 0噓 1→)

留言2則, 2人參與討論串2/2 (看更多)

※ 引述《lovemoyashi (被愛不如愛人)》之銘言： : Test 1 : 20. If a cube has an edge of length 10, then the length of the segment : connecting the center of a face of the cube to any vertex not contained : in the plane of that face is? : (a)√6 (b)6√5 (c) 5√6 (d) 3√5 (e) 10√6 : ans:c ----------------------- 建座標系, 令這個中心點座標為 (0,5,5), 而符合題目條件的頂點(對面那四個, 任取一即可), 我選 (10,10,10) 那個, 則此兩點距離為 [ (10-0)^2 +(10-5)^2 +(10-5)^2 ]^(1/2) = 5√6 ---------------------------- : Test 3 : 9. The sum of two numbers that differ by 1 is t. In terms of t, what : is the value of the greater of the two number : (a)(t-1)/2 (b) t/2 (c) (2t-1)/2 (d) t/2 + 1 (e) (t+1)/2 : ans:e ------------------------------ 令這二數為 x, x-1, 則 t = x + x-1 = 2x-1 so, x = (t+1)/2 ------------------------------- : Test 8 : 2. Paul wants to put up a 120-feet around three sides of his rectangular : garden and level a side unfenced. If the garden has the greatest area, how : many square feet of garden will Paul hedge around? : (a)1200 sq ft (b) 1800 sq ft (c) 2400 sq ft (d) 3000 sq ft (e) 3600 sq ft : ans:b ------------------------- 令這個缺一邊的長方形的三邊分別為 x, x, 120-2x 則面積為 x(120-2x) = -2x^2 + 120x = -2(x-30)^2 + 1800 所以面積最大值為 1800 -------------------------- : Test 13 : 21. 1< n < 5 : col a: the sum of the first n odd integers that are greater than zero : col b: n^2 -1 : ans:a -------------------------- 化簡一下 col a (它其實是個等比級數) col a = {1 + [1 + (n-1)*2 ]}*n/2 = n^2 > n^2-1 = col b p.s [ ]這東西包住的就是俗稱的下底 ----------------------- : 謝謝大家~ -- ※ 發信站: 批踢踢實業坊(ptt.cc) ◆ From: 220.139.40.34