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该死的英文, 总是让我有挫败感

sabre的马甲

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根据撒老师的说法,反函数并不改变x和y的关系。y=x 和 x=y 是一回事儿。 y=ax 和 x=y/a 也是一回事儿。
一回事儿的意思是关系不变,如果y和x是正比关系,辣x和y的反比关系恰恰不可能是正比关系的反函数。
在坐标上,转90度,图像没有变化,
 

shw019

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根据撒老师的说法,反函数并不改变x和y的关系。y=x 和 x=y 是一回事儿。 y=ax 和 x=y/a 也是一回事儿。
一回事儿的意思是关系不变,如果y和x是正比关系,辣x和y的反比关系恰恰不可能是正比关系的反函数。
太深奥了, 不懂。
我认为x, y的inverse关系, 应该是y=a/x。
 

sabre的马甲

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太深奥了, 不懂。
我认为x, y的inverse关系, 应该是y=a/x。
In mathematics, an inverse function (or anti-function[1]) is a function that "reverses" another function: if the function f applied to an input x gives a result of y, then applying its inverse function g to y gives the result x, and vice versa, i.e., f(x) = y if and only if g(y) = x.[2][3]

As an example, consider the real-valued function of a real variable given by f(x) = 5x − 7. Thinking of this as a step-by-step procedure (namely, take a number x, multiply it by 5, then subtract 7 from the result), to reverse this and get x back from some output value, say y, we should undo each step in reverse order. In this case that means that we should add 7 to y and then divide the result by 5. In functional notation this inverse function would be given by,

g ( y ) = y + 7 5 . {\displaystyle g(y)={\frac {y+7}{5}}.}

With y = 5x − 7 we have that f(x) = y and g(y) = x.

Not all functions have inverse functions. In order for a function f: XY to have an inverse,[nb 1] it must have the property that for every y in Y there must be one, and only one x in X so that f(x) = y. This property ensures that a function g: YX will exist having the necessary relationship with f.
Let f be a function whose domain is the set X, and whose image (range) is the set Y. Then f is invertible if there exists a function g with domain Y and image X, with the property:

f ( x ) = y ⇔ g ( y ) = x . {\displaystyle f(x)=y\,\,\Leftrightarrow \,\,g(y)=x.}

If f is invertible, the function g is unique,[4] which means that there is exactly one function g satisfying this property (no more, no less). That function g is then called the inverse of f, and is usually denoted as f −1.[nb 2]

Stated otherwise, a function, considered as a binary relation, has an inverse if and only if the converse relation is a function on the range Y, in which case the converse relation is the inverse function.[5]

Not all functions have an inverse. For a function to have an inverse, each element yY must correspond to no more than one xX; a function f with this property is called one-to-one or an injection. If f −1 is to be a function on Y, then each element yY must correspond to some xX. Functions with this property are called surjections. This property is satisfied by definition if Y is the image (range) of f, but may not hold in a more general context. To be invertible a function must be both an injection and a surjection. Such functions are called bijections. The inverse of an injection f: XY that is not a bijection, that is, a function that is not a surjection, is only a partial function on Y, which means that for some yY, f −1(y) is undefined. If a function f is invertible, then both it and its inverse function f−1 are bijections.

There is another convention used in the definition of functions. This can be referred to as the "set-theoretic" or "graph" definition using ordered pairs in which a codomain is never referred to.[6] Under this convention all functions are surjections,[nb 3] and so, being a bijection simply means being an injection. Authors using this convention may use the phrasing that a function is invertible if and only if it is an injection.[7] The two conventions need not cause confusion as long as it is remembered that in this alternate convention the codomain of a function is always taken to be the range of the function.

Example: Squaring and square root functions
The function f: ℝ → [0,∞) given by f(x) = x2 is not injective since each possible result y (except 0) corresponds to two different starting points in X – one positive and one negative, and so this function is not invertible. With this type of function it is impossible to deduce an input from its output. Such a function is called non-injective or, in some applications, information-losing.[citation needed]

If the domain of the function is restricted to the nonnegative reals, that is, the function is redefined to be f: [0, ∞) → [0, ∞) with the same rule as before, then the function is bijective and so, invertible.[8] The inverse function here is called the (positive) square root function.
 

oldbei

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今天又学了一个不可思议的词inverse, 是reversed 的意思。
为啥是不可思议?

俺想到一个相关的词儿:inverted 也是倒转,反转的意思。飞机和飞鸟的倒飞(肚皮朝上,背朝下,头朝前)叫inverted flying。倒车(轮子着地,车倒退)叫reverse driving, 所以, reverse 也可以当形容词用。辣reverse和reversed两个形容词的区别是啥涅?
 

oldbei

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男老师给女学生上课,想得好评, 最好是亲亲抱抱?! 傻了。:eek:o_O
亲亲抱抱是方法之一,还一种是装。你越是不懂,奏越是给你一大堆更深奥的东东,目的不是让你懂,而是让你产生一种崇拜的赶脚。:ROFLMAO::ROFLMAO::ROFLMAO:
 

oldbei

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太深奥了, 不懂。
我认为x, y的inverse关系, 应该是y=a/x。
所以俺经常提醒自己不能望文生义呢。看上去,你是对“反”这个字有鸟先入为主的解读。

基督和反基督(敌基督)是两个完全不同,完全相反的东东。但把保罗倒钉在十字架上,他还是保罗。反函数类似于从另一个视角看函数中两个变量的关系,看的其实是同一个关系,相当于说你的工资是俺的两倍,或者说俺的工资是你的一半。正反两种说法,说的是一回事儿。
 

oldbei

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阅读的时候, 有些词知道意思, 但读音要查。
以前练听说太难了。小的时候有个邻家, 在工厂上班, 想学学英文, 找我问banana 的读音。我当时太innocent 了, 否则不会教他的。
这是闲话, 我要表达的意思是, 这种学习条件,他学会300词的难度是相当大的。
分享一个俺最近才猜意识到的读音:sleight要读成slight,而不是slate。为啥eight和sleigh中eigh都发成【A】,而在sleight里突然发成【I】鸟?:cry::cry::cry:
 

shw019

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为啥是不可思议?

俺想到一个相关的词儿:inverted 也是倒转,反转的意思。飞机和飞鸟的倒飞(肚皮朝上,背朝下,头朝前)叫inverted flying。倒车(轮子着地,车倒退)叫reverse driving, 所以, reverse 也可以当形容词用。辣reverse和reversed两个形容词的区别是啥涅?
当时不知道inverse啥意思, 一查是reversed, 同义词, 都有-verse, “前缀”不同,当时 觉得奇怪。

reverse是反向的,那reversed就是被反转了的意思。
 

shw019

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分享一个俺最近才猜意识到的读音:sleight要读成slight,而不是slate。为啥eight和sleigh中eigh都发成【A】,而在sleight里突然发成【I】鸟?:cry::cry::cry:
sleight s-l-eigh-t
slight s-ligh-t

sleigh s-l-eigh
eight eigh-t
我会把sleight, sleigh都读成-eigh的音。
 

bloodwolfmoon

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今天问了一下老外,one shot deal意思是指“一辈子只买一次”,例如房子家具结婚戒指什么的。

一锤子买卖怎么说,讨论了半天都没有找到明确的单词短语,最后干脆说"再也不去那里购买了“。
可以理解成“你只能骗我一次”吗?
You can only fool me once
 
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也叫反函数,
y = ax + b,
反函数是, x = (y-b)/a,

指数函数和对数函数, 互为反函数,
大错特错,x=(y-b)/a只不过是方程y=ax+b的解而已,把解裡的x和y的位置掉转过来才叫反函数,所以反函数是y =(x-b)/a才对。

这可是高中数学的基础中的基础,可没有人会把这种定义层次的东西给搞错的。

老萨就是爱tm装什么学识长者,长期被他洗脑的粉丝们连他说话内容的是非都确证不好动不动就赞他了。看到这种初步错误,我都不信他是读过清华的。
 
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