【正文】 ,且 2 2 2 3a b c ab? ? ? . (Ⅰ) 求 A 。 (Ⅱ )若 42a? , 5b? ,求向量 BA 在 BC 方向上的投影 . 【答案】 解 :(Ⅰ) 由 3c os ( ) c os sin ( ) sin ( ) 5A B B A B A c? ? ? ? ? ? 得 53s in)s in (c o s)c o s ( ????? BBABBA , 則 53)c os( ???? BBA ,即 53cos ??A 又 ???A0 ,則 54sin ?A (Ⅱ )由正弦定理 ,有 BbAa sinsin ? ,所以22sinsin ?? a AbB, 由題知 ba? ,則 BA? ,故 4??B . 根據(jù)余弦定理 ,有 )53(525)24( 222 ?????? cc, 解得 1?c 或 7??c (負(fù)值舍去 ), 向量 BA 在 BC 方向上的投影為 ?BBAcos 22 37． （ 2020 年高考江西卷（文）） 在 △ABC 中 ,角 A,B,C 的對(duì)邊分別為 a,b,c,已知 sinAsinB+sinBsinC+cos2B=1. (1)求證 :a,b,c 成等差數(shù)列 。 (Ⅱ) 若 △ ABC 的面積 53S? , 5b? ,求 sin sinBC的值 . 【答案】 (Ⅰ) 由 co s 2 3 co s( ) 1A B C? ? ?,得 22 co s 3 co s 2 0AA? ? ?, 即 ( 2 c o s 1)(c o s 2 ) 0AA? ? ?,解得 1cos2A? 或 cos 2A?? (舍 去 ). 因?yàn)?0 πA??,所以 π3A?. (Ⅱ) 由 1 1 3 3s i n 5 3 ,2 2 2 4S b c A b c b c? ? ? ? ?得 20bc? . 又 5b? ,知 4c? . 由余弦定理得 2 2 2 2 c o s 2 5 1 6 2 0 2 1 ,a b c b c A? ? ? ? ? ? ?故 21a? . 又由正弦定理得 22 2 0 3 5s in s in s in s in s in 2 1 4 7b c b cB C A A Aa a a? ? ? ? ? ?. 39． （ 2020 年高考安徽（文）） 設(shè)函數(shù)( ) si n si n( )3f x x x ?? ? ?. (Ⅰ) 求()fx的最小值 ,并求使()取得最小值的 x的集合 。 然后xsin3?向左平移6?個(gè)單位 ,得)6sin()( ?xxf 40． （ 2020年高考北京卷（文）） 已知函數(shù) 2 1( 2 c os 1 ) sin 2 c os 42f x x x x? ? ?（ ） . (I)求 fx（ ） 的最小正周期及最大值 。 (2)令 2?? ,將函數(shù) ()y f x? 的圖像向左平移 6? 個(gè)單位 ,再往上平移 1個(gè)單位 ,得到函數(shù) ()y gx? 的圖像 .對(duì)任意的 aR? ,求 ()y gx? 在區(qū)間 [ , 10 ]aa ?? 上零點(diǎn)個(gè)數(shù)的所有可能值 . 【答案】 法一 :解 :(1) ( ) 2 sin 2 sin( ) 2 sin 2 c os 2 2 sin( )24F x x x x x x??? ? ? ? ? ? ? ()Fx是非奇函數(shù)非偶函數(shù) . ∵ ( ) 0 , ( ) 2 244FF??? ? ?,∴ ( ) ( ) , ( ) ( )4 4 4 4F F F F? ? ? ?? ? ? ? ? ∴ 函數(shù) ( ) ( ) ( )2F x f x f x ?? ? ?是既不是奇函數(shù)也不是偶函數(shù) . (2) 2?? 時(shí) , ( ) 2sin 2f x x? , ( ) 2 sin 2 ( ) 1 2 sin ( 2 ) 163g x x x??? ? ? ? ? ?, 其最小正周期 T?? 由 2 si n( 2 ) 1 03x ?? ? ?,得 1sin( 2 )32x ?? ? ?, [來(lái)源 :學(xué) ,科 ,網(wǎng) ] ∴ 2 ( 1 ) ,36kx k k Z???? ? ? ? ? ?,即 ( 1 ) ,2 12 6kkx k Z? ? ?? ? ? ? ? ? 區(qū)間 ? ?, 10aa ?? 的長(zhǎng)度為 10 個(gè)周期 , 若零點(diǎn)不在區(qū)間的端點(diǎn) ,則每個(gè)周期有 2 個(gè)零點(diǎn) 。 故當(dāng) ( 1 ) ,2 12 6kka k Z? ? ?? ? ? ? ? ?時(shí) ,21 個(gè) ,否則 20 個(gè) . 法二 : 42． （ 2020 年高考遼寧卷（文）） 設(shè)向量 ? ? ? ?3 si n , si n , c os , si nx , 0 , .2a x x b x x ???? ? ? ???? (I)若 .a b x? 求 的 值 ； (II)設(shè)函數(shù) ? ? ? ?,.f x a b f x? 求 的 最 大 值 【答案】 （英文版 ） easily blame, to prevent the broken window effect. Supervise the leading cadres to play an exemplary role, take the lead in the strict implementation of the code and rule , lead to safeguard the solemnity and authority of the party discipline, ensure that the party discipline and the laws and regulations for implementation in place. Throughout the discipline in the daily supervision and management , strengthen supervision and inspection, from the thorough investigation of violations of discipline behavior. Strengthen to key areas, key departments and key projects as well as the masses reflect the concentration of the units and departments for supervision. strengthening supervision, discipline inspection and supervision of cadres to set an example for pliance with the code and rule is a man must be hexyl, blacksmith needs its own hardware. Discipline inspection ans as the executor of the party discipline, and supervisor of the defenders, for its supervision must be more strictly, discipline inspection and supervision of cadres to firmly establish the awareness of Party Constitution, sense of discipline and rules consciousness, politics loyalty, sense obey. Action speak Ji Ordinance to set an example of the regulations of the rule of law, strengthen supervision and accept the supervision of the firmness and consciousness, do ply with and . To firmly establish the discipline must first be disciplined, the supervisor will be subject to the supervision of concept, and consciously safeguard and implement party passes party, take the lead in practicing three strict real strict, so loyal, clean, play. To be good at learning, the Constitution and the code as morality, politics and brought to fruition。 to discipline a ruler, often the control inspection, and consciously in the ideological red line to draw the row Ming Good accumulation is indeed the bottom line, so that the heart has fear, said to have quit, the line has ended. Attached: indifferent to heart, calmly to the table in our life, there are many unpredictable things will happen, some good, some bad things, we cannot control is powerless to stop, but with time, you will find in life sometimes turns out to be not good, some bad things finally turned out to be a good thing, but then we muddy however did not know, this is the life teach us things. 1, life can be plex, can also be simple. Want simple life of precipitation, to have enough time to reflect, to make Bee more perfect. Life is the most important thing is not to win, but the struggle。 not disillusioned after the heart, such as ashes, but experience the storm after the enlightenment。t always take everything back to things, and don39。t want to face, don39。 I am not afraid of the truth to tell the best friend, I39。t 6, when we are in a positive frame of mind, you will find many good things。 life happy and worry, all is you of life attitude, optimistic, good luck。 heart tired, calm. Grow up, mature, this society read. Tired and sad, squat down, to their a hug. Because the world no one can sympathize with you, have mercy on you. You cry, tears is your own。 now want anything, for fear that others know, or like to lose the same. 9, the heart move, everything in the world is followed by birth, Rangrang, important thing is often the most difficult to open one39。 to let strangers people care about your life in the good things, the original is not easy 10, do not blame, do not laugh at who, also don39。 no matter how many grievances, how unfortable, and