第16章 速解技巧（1 / 2）

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aaagtbaagt1，p=√(lga·lgb)，q=(lga+lgb)/2，r=lg(a+b)/2，则

a.qaagtpaagtr

b.raagtqaagtp

c.raagtpaagtq

d.qaagtraagtp

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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