查看“︁婆羅摩笈多”︁的源代码

{{Infobox person
|name        = 婆羅摩笈多
|image       = Hindu astronomer, 19th-century illustration.jpg
|image_size  = 
|caption     = 
|birth_date  = 598年
|birth_place = [[哈尔沙帝国]][[拉贾斯坦邦]][[宾马尔]]
|death_date  = 670年
|death_place = [[瞿折羅-普羅蒂訶羅]]
|occupation  = [[印度]][[数学家]]和[[天文学家]]
}}
'''婆羅摩笈多'''（{{lang-sa|'''ब्रह्मगुप्त'''}}，[[IAST]]: {{IAST|'''Brahmagupta'''}}，{{bd|598年||668年||catIdx=B}}），[[印度]][[数学家]]和[[天文学家]]，生於印度[[拉贾斯坦邦]][[宾马尔]]<ref name="Seturo_2003"/>，一生可能大多数时间都在生地度过。当时，該地隸屬于[[哈尔沙帝国]]。婆羅摩笈多為[[乌贾因]][[天文台]]台长，於任职期间著書二部，乃关于[[数学]]和[[天文学]]，當中包括於628年寫成的《{{link-en|婆罗摩历算书|Brāhmasphuṭasiddhānta}}》。

婆羅摩笈多係首位提出[[0]]計算規則的數學家。和當時許多的印度數學家一樣，會將文字編排成橢圓形的句子，而且最後會有一個環狀排列的詩。由於未提出證明，不知其中的數學推導過程<ref>{{Cite web 
 |url=http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Brahmagupta.html 
 |title=Brahmagupta biography 
 |accessdate=2013-07-15 
 |publisher=School of Mathematics and Statistics University of St Andrews, Scotland 
 |archive-date=2013-09-15 
 |archive-url=https://www.webcitation.org/6Jeq9449q?url=http://www-groups.dcs.st-and.ac.uk/~history/Biographies/Brahmagupta.html 
 |dead-url=yes 
 }}</ref>。

==生平和著作==
在《婆罗摩历算书》第十四篇的第7句及第8句，提及婆羅摩笈多於三十歲著作此書，也是628年<!--Śaka 550 during the reign of King Vyāghramukha-->，便可推得婆羅摩笈多是在598年出生<ref>{{cite book
 |title=Census of the Exact Sciences in Sanskrit (CESS) 
 |author=David Pingree
 |publisher=American Philosophical Society
 |pages=p254
}}</ref>
<ref name="Seturo_2003">{{cite book
 |title=''Brāhmasphuṭasiddhānta'' (CH. 21) of Brahmagupta with Commentary of Pṛthūdhaka, critically edited with English translation and notes 
 |author=Seturo Ikeyama
 |publisher=INSA
 |year=2003
}}</ref>。婆羅摩笈多寫了四本有關數學及天文學的書，分別為624年的《Cadamekela》、628年的《{{link-en|婆罗摩历算书|Brāhmasphuṭasiddhānta}}》、665年的《Khandakhadyaka》及672年的《Durkeamynarda》，其中最著名的是《婆罗摩历算书》。波斯歷史學家[[比魯尼]]在其著作《Tariq al-Hind》提到，[[阿拉伯帝國]][[阿拔斯王朝]]的[[哈里發]][[阿布·阿拔斯·阿卜杜拉·馬蒙·本·哈倫|馬蒙]]曾派大使到印度，並將一本「算書」帶到巴格達，翻譯為阿拉伯文，一般認為這本算書就是《婆罗摩历算书》<ref name="Boyer Siddhanta">{{Cite book|last=Boyer|authorlink=Carl Benjamin Boyer|title=|year=1991|chapter=The Arabic Hegemony|pages=226|quote=By 766 we learn that an astronomical-mathematical work, known to the Arabs as the ''Sindhind'', was brought to Baghdad from India. It is generally thought that this was the ''Brahmasphuta Siddhanta'', although it may have been the ''Surya Siddhanata''. A few years later, perhaps about 775, this ''Siddhanata'' was translated into Arabic, and it was not long afterwards (ca. 780) that Ptolemy's astrological ''[[Tetrabiblos]]'' was translated into Arabic from the Greek.}}</ref>。

== 数学 ==
《婆罗摩历算书》中，有四章半講述纯数学，第12章講述演算系列和少许几何学。第18章是关于代数，婆羅摩笈多在这里引入了一个解二次[[丟番圖方程]]如''nx''²&nbsp;+&nbsp;1&nbsp;=&nbsp;''y''²的方法。

婆羅摩笈多还提供了计算任何四边已知的[[圆内接四边形]]的面积的公式。[[海伦公式]]是婆羅摩笈多给出的公式的一个特殊形式（一边为零）。[[婆羅摩笈多公式]]与海伦公式之间的关系，类似[[餘弦定理]]扩展了[[勾股定理]]。

===代數===
婆羅摩笈多在《婆羅摩曆算書》第十八章給了[[線性方程]]的解：

<blockquote>
[[色 (佛教)|色]]之間的數交換後的差除以未知數的差，就是[[方程]]的解。<ref name="Plofker Chapter 18 Brahmasphutasiddhanta">{{Harv|Plofker|2007|pp=428–434}}</ref></blockquote>

當中方程<math> b x + c = d x + e</math>的解是<math>x = \tfrac{e-c}{b-d}</math>，而色是指常數項c和e。他然後進一步給了[[二次方程]]兩個解：

<blockquote>
18.44：色和二次項和4相乘的積加一次項的二次方的數，把這個數開方後減一次項，再把整個數除一次項的2倍，就是方程的解。<ref group="注">英文原文是：“18.44. Diminish by the middle [number] the square-root of the rupas multiplied by four times the square and increased by the square of the middle [number]; divide the remainder by twice the square. [The result is] the middle [number].”</ref><br />
18.45：色和二次項的積加一次項一半的二次方的數，把這個數開方後減一次項的一半，再把整個數除一次項就是方程的解。<ref group="注">英文原文是：“18.45. Whatever is the square-root of the rupas multiplied by the square [and] increased by the square of half the unknown, diminish that by half the unknown [and] divide [the remainder] by its square. [The result is] the unknown.”</ref><ref name="Plofker Chapter 18 Brahmasphutasiddhanta" />
</blockquote>

其實它們分別說了方程<math>a x^2 + b x = c</math>的解恆等於
:<math>x = \frac{\sqrt{4ac+b^2}-b}{2a} </math>
和
:<math>x = \frac{\sqrt{ac+\tfrac{b^2}{4}}-\tfrac{b}{2}}{a} </math>。

=== 運算 ===
==== 級數 ====
婆羅摩笈多提供了頭<math>n</math>個平方和及立方和的算法：
<blockquote>
12.20. 平方和是[头几个整数直接和]乘以两倍[项数]与1的和后再[[除以3]]的结果。立方和是这直接和的平方。<ref group="注">英文原文是：“12.20. The sum of the squares is that [sum] multiplied by twice the [number of] step[s] increased by one [and] divided by three. The sum of the cubes is the square of that [sum] Piles of these with identical balls [can also be computed]”</ref><ref name="Plofker Brahmagupta quote Chapter 12">{{Harv|Plofker|2007|pp=421–427}}</ref>
</blockquote>

婆羅摩笈多的方法較近似於現代形式。

這裏，婆羅摩笈多所給的頭<math>n</math>個自然數的平方和立方的算法，分別為<math>\tfrac{n(n+1)(2n+1)}{6}</math>和<math>[\tfrac{n(n+1)}{2}]^2</math>

==== 零 ====
婆羅摩笈多普及了數學中的重要概念：[[0]]。《婆羅摩曆算書》是至今為止，已知首部將0視為普通數字使用之著作。除此之外，這部書還闡述了[[負數]]和0的[[運算]]規則。這些規則與現代規則非常接近。

婆羅摩笈多在《婆羅摩曆算書》第十八章中這樣提到：
<blockquote>
18.30：正數加正數為正數，負數加負數為負數。正數加負數為他們彼此的差，如果它們相等，結果就是零。負數加零為負數，正數加零為正數，零加零為零<ref group="注">英文原文是：“18.30. [The sum] of two positives is positives, of two negatives negative; of a positive and a negative [the sum] is their difference; if they are equal it is zero. The sum of a negative and zero is negative, [that] of a positive and zero positive, [and that] of two zeros zero.
[...]”</ref><br>
18.32：負數減零為負數，正數減零為正數，零減零為零，正數減負數為他們彼此的和。<ref group="注">英文原文是：“18.32. A negative minus zero is negative, a positive [minus zero] positive; zero [minus zero] is zero. When a positive is to be subtracted from a negative or a negative from a positive, then it is to be added
[...]”</ref><ref name="Plofker Chapter 18 Brahmasphutasiddhanta"/>
</blockquote>

他這樣描述乘法：
<blockquote>
18.33：正負得負，負負得正，正正得正，正數乘零﹑負數乘零和零乘零都是零。<ref group="注">英文原文是：“18.33. The product of a negative and a positive is negative, of two negatives positive, and of positives positive; the product of zero and a negative, of zero and a positive, or of two zeros is zero.”</ref><ref name="Plofker Chapter 18 Brahmasphutasiddhanta"/>
</blockquote>

最大的區別在於，婆羅摩笈多試圖定義[[除以零]]，在現代數學中這個運算無解。
<blockquote>
18.34：正數除正數或負數除負數為正數，正數除負數或負數除正數為負數，零除零為零<ref group="注">英文原文是：“18.34. A positive divided by a positive or a negative divided by a negative is positive; a zero divided by a zero is zero; a positive divided by a negative is negative; a negative divided by a positive is [also] negative.”</ref><ref name="Plofker Chapter 18 Brahmasphutasiddhanta"/><br>
18.35：正數或負數除以零有零作為該數的除數，零除以正數或負數有正數或負數作為該數的除數。正數或負數的平方為正數，零的平方為零。<ref group="注">英文原文是：“18.35. A negative or a positive divided by zero has that [zero] as its divisor, or zero divided by a negative or a positive [has that negative or positive as its divisor]. The square of a negative or of a positive is positive; [the square] of zero is zero. That of which [the square] is the square is [its] square-root.”</ref><ref name="Plofker Chapter 18 Brahmasphutasiddhanta"/>
</blockquote>
婆羅摩笈多的定義不實用，比如他認為<math>\tfrac{0}{0} = 0</math>。而他並沒有保證<math>\tfrac{a}{0}</math>且<math>a \neq 0</math>的說法是對的。<ref name="Boyer Brahmagupta p220">{{Cite book|last=Boyer|authorlink=Carl Benjamin Boyer|title=|year=1991|chapter=China and India|pages=220|quote=However, here again Brahmagupta spoiled matters somewhat by asserting that <math>0 \div 0 = 0</math>, and on the touchy matter of <math>a \div 0</math>, he did not commit himself:}}</ref>

=== 幾何 ===
==== 婆羅摩笈多公式 ====
[[Image:Brahmaguptas formula.svg|200px|thumb|right|圖供參考]]
{{Main|婆羅摩笈多公式}}

婆羅摩笈多在《婆羅摩曆算書》第十二章中這樣提到
<blockquote>
12.21：一個四邊形或三角形的大約面積是邊和對邊的和的一半。四邊形的準確面積是每一個邊分別地被另外三條邊減的和的一半的開方。<ref group="注">英文原文是：“12.21. The approximate area is the product of the halves of the sums of the sides and opposite sides of a triangle and a quadrilateral. The accurate [area] is the square root from the product of the halves of the sums of the sides diminished by [each] side of the quadrilateral.”</ref><ref name="Plofker Brahmagupta quote Chapter 12"/>
</blockquote>

設一個圓內接四邊形的四條邊為''p''﹑''q''﹑''r''﹑''s''，大約面積為<math>(\tfrac{p + r}{2}) (\tfrac{q + s}{2})</math>，設<math>t = \tfrac{p + q + r + s}{2}</math>，準確面積則為<math>\sqrt{(t - p)(t - q)(t - r)(t - s)}.</math>。

雖然婆羅摩笈多並沒有說四邊形為[[圓內接四邊形]]，但其實這是明顯的。<ref>{{Harv|Plofker|2007|p=424}} Brahmagupta does not explicitly state that he is discussing only figures inscribed in circles, but it is implied by these rules for computing their circumradius.</ref>

==== 圆周率 ====
婆羅摩笈多還提供了一個[[化圓為方]]的幾何方法：
<blockquote>
12.40：直徑和半徑的二次方每個乘3分別地為圓形大約的周界和面積。而準確值則為直徑和半徑的二次方乘開方10。<ref group="注">英文原文是：“12.40. The diameter and the square of the radius [each] multiplied by 3 are [respectively] the practical circumference and the area [of a circle]. The accurate [values] are the square-roots from the squares of those two multiplied by ten.”</ref><ref name="Plofker Brahmagupta quote Chapter 12"/>
</blockquote>

这个方法不十分精确，按照它的计算得出的[[圆周率]]为<math>\pi=\sqrt{10}\approx3.162</math>。

== 天文学 ==
婆羅摩笈多是最早使用代数解决天文问题的人。一般认为，阿拉伯人是通过《婆罗摩历算书》了解到印度天文学的<ref>{{Cite web |url= http://www-groups.dcs.st-and.ac.uk/~history/Projects/Pearce/Chapters/Ch8_3.html |title= Brahmagupta, and the influence on Arabia |accessdate= 2013-07-15 |publisher= School of Mathematical and Computational Sciences University of St Andrews |date= 2002-05 |archive-date= 2013-09-15 |archive-url= https://www.webcitation.org/6Jeq9hMCc?url=http://www-groups.dcs.st-and.ac.uk/~history/Projects/Pearce/Chapters/Ch8_3.html |dead-url= no }}</ref>。770年，[[阿拔斯王朝]]第二代哈里发[[曼苏尔]]邀请乌贾因的学者赴[[巴格达]]，使用《婆罗摩历算书》介绍印度代数天文学。他还请人将婆羅摩笈多的著作译成阿拉伯语。

婆羅摩笈多其它重要的天文成就在于：计算[[星曆表]]、天体出生和下降的时间、[[合相]]、[[日食]]和[[月食]]的方法。婆羅摩笈多批评[[往世书]]中大地平坦或者像碗一样中空的理论。相反地，他的观察认为大地和天空是圆的，不过他误认为大地不运动。

==相關條目==
*[[婆罗摩笈多－斐波那契恒等式]]
*[[婆羅摩笈多公式]]
*[[婆羅摩笈多定理]]
*[[婆什迦羅第二]]

== 原文引注 ==
{{Reflist|2|group="注"}}

==參考資料==
{{Commonscat|Brahmagupta}}
{{Portal box|印度|天文学|数学|人物}}
{{reflist}}

{{Authority control}}
[[Category:印度数学家]]
[[Category:印度天文学家]]