第16章 速解技巧
天赋系男神 作者:佚名
第16章 速解技巧
二模之后,高三1班出了个顶级黑马的消息,一石激起千层浪。非但光速传遍了文理科的十个班,洛北本人还被当做珍奇异兽也似,走到哪里都有人边瞅他边小声议论:
“看见没,那个就是1班的生猛牛人,两个月逆袭了八十分!”
就连他的座位,也似乎变成了一个热门景点。不时会有人拿著习题,以“答疑”的名义,凑到他身边来问东问西。其中一些人,甚至是以往见了面,都不会打招呼的傢伙。
他们的来意,倒不是那么难猜。与其说是请教,倒不如说是考较,想看看这匹突然杀出来的阿巴嘎马,是有真本事,还是搞了什么邪道招。
起初,洛北还算有问必答。解答別人的疑难,也能获得“做题家”经验,只是性价比偏低——每解答五个旁人的问题,才能获得可怜的1点经验值,效率远低於刷模考卷。
但发现旁人问的都是些没有挑战性甚至乏味的题目,他一讲二讲还是不明白时,洛北开始烦了。
他不像路行舟,没有“舟神”包袱,更没有解答的义务。
时间……时间才是对他而言,最贵重之物。
这天晚自习,洛北还在解一道复杂的立体几何题。辅助线已经画好,灵感正如泉涌。
“那、那啥,北哥。”有人在旁边笑嘻嘻地说著,打断了他的思路。
洛北抬头,是张不太眼熟的脸。
俞启瑞,一个平时跟他连点头之交都算不上的男生。提问积极,上课活跃,是老师讲题时捧哏的常客。听著听著,他还会不时冒出句“哦,懂了懂了”、“切,这么简单,我早就知道”的暴论,是班里有名的“懂哥”。
身为走读生的俞启瑞,也特別擅长给同窗施加无形压力。他平时最爱聊的话题是“昨晚我做题做到凌晨两点半”、“我妈说她看了就心疼”以及“不是,这么简单的题都有人不会?我呆了”。
不过,虽然大部分时间都在致力於塑造自己“卷王”的形象,俞启瑞却是那种看起来非常努力,笔记本记得密密麻麻,但成绩却不怎么见起色的类型。
“怎么?”洛北问,看见俞启瑞把一个本子塞到他的面前。
又是问题。
“北哥,帮看看这第12题选择。”俞启瑞全然不顾当初他跟洛北一点不熟,嬉皮笑脸地说。
甚至都没有问他有没有空。
洛北皱了皱眉,瞥了眼题目。这是一道不等式:
若aamp;amp;gt;bamp;amp;gt;1,p=√(lga·lgb),q=(lga+lgb)/2,r=lg(a+b)/2,则
a. qamp;amp;gt;pamp;amp;gt;r
b. ramp;amp;gt;qamp;amp;gt;p
c. ramp;amp;gt;pamp;amp;gt;q
d. qamp;amp;gt;ramp;amp;gt;p
常规解法的话,需要利用均值不等式,对p、q、r依次比较大小。不是什么难题,但得动笔算算。
不过,洛北一眼看出,这道题正好可以通过特殊值法速解,两秒就能心算出来。
如此甚好,他可懒得在这个不知所谓的傢伙身上浪费时间。
“选b。”几乎是瞬间,洛北给出了答案。
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“唔……怎么算的?”
俞启瑞看看自己手里的京师大附中金卷,又瞟瞟洛北,满腹狐疑:他怎么解得这么快?难道是做过的题?
“你直接取a=100,b=10,那么就有p=√2,q=1.5=lg√1000,r=lg55=lg√3025,选b不是很明显吗?”洛北说。
“啊?这样也行?”听意料之外的答案从洛北的嘴里蹦了出来,俞启瑞不禁瞠目结舌,“不是,我是问你正经思路呢,別逗。”
“这就是正经思路。”洛北不耐烦跟他瞎扯,“你就说对不对吧?”
“是选b没错啦,但你这样是钻题目空子吧?”俞启瑞没得到想要的答案,开始抬槓,“你这不就是取巧吗?能不能讲讲正规的解法?这种歪门邪道,考试时万一老师变一变题目,不適用那不就白瞎啦?”
按洛北这样解確实能选出答案,但是做法不普適啊。下一回不能用特殊值法怎么办?
“能做对就行。”洛北的耐心彻底耗光了,“你想用正攻的话,就均值不等式。自己推去。”
“我……你……那我要怎样,才能想到用均值不等式啊?从题面联想到均值不等式的思路,能说说么?”俞启瑞不依不饶。
洛北的声音开始转冷:“我要做题了,去问吕老师,他会给你讲得比我清楚一百倍。”
他不再理会俞启瑞,重新低下头,续接刚才中断的思路。
俞启瑞碰了一鼻子灰,脸上掛不住,悻悻然地回到自己座位。
他左思右想,就是咽不下这口气,於是跟同桌嘀嘀咕咕:“有什么了不起的,考好一次就翘尾巴了?暴发户心態!讲题都藏私,用的还是歪路子,跟人家路行舟根本没得比。舟神那才叫真才实学,有本事他是真教!”
他的声音不大不小,於是恰好被不远处的萧微薇,还有路过收班费的班长老唐听了个正著。
萧微薇的秀眉瞬间蹙了起来,心里很不舒服。明明说的不是自己,她却下意识想开口,替洛北辩解几句。
可话到嘴边,她又迟疑了。
自从上次那场“告白”风波之后,班里总有些人在背后偷偷议论,传著各种她“追求洛北未果”的式八卦。
虽然……暗恋洛北这件事,確实是真的。但骄傲如她,也绝不愿意在別人眼中,变成一个上赶著倒贴的“舔狗”。
就在迟疑间,老唐把登记簿往旁边的桌子一放,走过来拍拍俞启瑞的肩膀:“行了,別再嘰嘰歪歪了。都高三的人了,多少知道点分寸吧?帮忙解答问题,是情分不是本分。洛北他自己也要复习,他占用了本该做题的时间帮你解答,你怎么还不爽上了?”
“我不是不爽!”俞启瑞不服气地爭辩,“我是觉得他那样解不对!哪有这样钻空子的?吕老师教过……”
“停!”老唐也烦了,他挥了挥手,打断了对方的喋喋不休,“你觉得哪里不明白,你就去问老师,行吗?节省大家的时间,两全其美。”
“沆瀣一气!”俞启瑞嘀咕了一句,但终究不敢跟班长正面硬刚,抱著自己的习题册,气鼓鼓地真的朝著办公室的方向走去了。