Finding Cube Roots: Vedic Mathematics

Contributed by:

Harshdeep Singh Fri, Apr 08, 2022 12:56 PM UTC

This PDF contains :
Introduction,
Unitary Method,
Vedic Method

1. FINDING CUBE ROOTS: NEPALI AND VEDIC METHODS
Jayanta Acharya
Mathematics is a study of quantity, structure, space and change. More specifically it is the study
of Arithmetic, Algebra, Geometry and Analysis. Many students find mathematics a difficult and
boring subject. If we use different methods to solve the same problem, students may come to
enjoy the subject. Vedic Mathematics is becoming increasingly popular as more and more people
are introduced to the beautifully unified and easy Vedic methods.
Finding the cube root of any number is a very difficult task for students. It is the reciprocal
procedure of calculating the cube. If 8 is the cube of 2, then the cube root of 8 is 2. If 27 is the
cube of 3, then the cube root of 27 is 3 and so on.
Unitary Method
Masny arithmetic problems can be solved by the unitary method but for finding square, square
root, cube and cube root we cannot use unitary method. Bhaskara says
वग# वग#पदं घनं घनपदं सं#य%य यद् ग"यते
तत् !ैरािशकमेव भेदब%लं ना#यत् ततेा िव#ते ।
एतद् यद् ब"दा%मदा'दजडधीधीवृि/बु12ा बुधै
िव#$द&'चक*ारचा-मितिभः पाटीित ति#िम%तम् ।। ( िश#दा&तिशरेामिण !"ना%याय )
(Whatever we say about square, square root, cube and cube root, expect them the patiganitam is
nothing but different forms of unitary method.)
The unitary method is a technique which used for solving a problem by finding the value of a
single unit and then finding the necessary value by multiplication of the single unit value.
If the cost of 5 liters of oil is Rs 25 then find the cost of 80 liter of oil. For such question we
use unitary method
the cost of 5 liters of oil is Rs 25
25
the cost of 1 liter of oil is Rs =5
5

2. 25
the cost of 80 liters of oil is Rs × 80 = 400
5
But for the case of cube this does not work.
If the cube of 2 is 8 then find the cube of 4?
8
The cube of 2 is 8, then, by proportion, the cube of 1 would be = 4 in which case the cube
2
8
would be × 4 = 16.
2
The same is true for finding a cube root inasmuch as simple proportion using the untary method
does not work.
In this context, we discuss the method introduced by a Nepali scholar Gopal Pandey. He claims
that the cube root can also be calculated by unitary method.
Gopal Pandey was a popular scholar of ancient mathematics in his commentary. His praise in
local language Nepali can be seen in this form,
गेाखा%का मिणरामका सुत बडा या#ी बलीराम् भया
ित#का पु#ः िहतै !वदेशीजनक*ा ग"या% त गेापाल् भया ।
!ाचीन् सब् किड खेाल् !द#या अित असल् !"थै बनाइ%दया
ितन् ले !य#गिणत् सहज् ग"र"दया स"नह% खुस् भया ।।
Maniram's grandson and Baliram's son, Gopal Pandey, was from Gorkha and he wrote a
manual of Arithmetic in Nepali. Bakyatya Chandrika (1895 AD) in Nepali and later on
translated into Hindi.
His method is very useful and similar to Vedic method. His method is explained by examples in
the following paragraphs.
Example: What is the cube root of 1728?
Place dots above the first digit on the right and then above every fourth digit. For 1728 the dots
should be above 8 and 1.
! 8!
172
− 1000
728

3. If there are two dots the answer is of two digits and, by observing, we can guess that the answer
must be between 10 to 20, because the cube of 10 is 1000 and the cube of 20 is 8000. 1728 is
between 1000 to 8000 so the answer is between 10 and 20. Pandey says since the difference of
two cubes is (8000 - 1000 =) 7000, the difference of cube root is (20 – 10 = ) 10 .
Find the difference of the given number, 1728, and the cube of 10 (i.e. 1728 - 1000 = 728)
Now Pandey says use the unitary method like this,
Since the difference in two cubes is 7000 then the difference of two cube roots is 10.
If the difference in two cubes is 1 then the difference of two cube roots is 10/7000
28
If the difference in two cubes is 728 then the difference of two cube roots is 1
700
This indicates that the next digit must be greater than 1 and it should be less than 2. Pandey says
the last digit must be 2 and the final answer must be 12.
Vedic Method
Example: Find the cube root of 2197
First make a group of three digits from the right 2 | 197
The cube ends in 7 and so the cube root will end with a 3. We will put 3 as the right hand part of
the answer. For the first part of the answer look at the second part of the separation of given
number there is 2 which lies between cube of 1 and 2 i.e. 1 and 8. The smaller number is 1,
which we will put as the left hand part of the answer. Final answer is 13.
Example: Find the cube root of 1157625
Separate off three digits from the right, 1157 | 625. Since 1157625 ends with a 5 so the cube root
also ends with a 5. The number to the left of the separation, 1157, lies between the cube of 10
(1000) and the cube of 11 (1331).
Out of 10 and 11, we take the smaller number 10 and put it beside the 5 already obtained. The
final answer is 105.
The same problem is solved by using Nepali Unitary method (Pandey method ) as follows:
Place the dot from the last digit of the given number and repeat it leaving two digits. For
1157625 the dot should be above 5, 7 and 1 so the cube root of the given number is of three
1! 1 5 7! 6 2 5!
1
15 7 6 2 5

4. The answer must be between 100 to 110 because the cube of 100 is 1000000 and the cube of 110
is 1331000. Pandey says, if the difference of two cubes is 1000000 - 1331000 = 331000, the
difference of cube roots is 110 - 100 = 10.
Find the difference of the given number and the cube of 100 (i.e. 1157625 -1000000 = 157625)
Now Pandey uses the unitary method like this,
If the difference in two cubes is 331000 then the difference of two cube roots is 10.
If the difference in two cubes is 1 then the difference of two cube roots is 10/331000.
25225
If the difference in two cubes is 157625 then the difference of two cube roots is 4
33100
This indicates that the next digit must be greater than 4 and it should be less than 5. Pandey says
the last digit must be 5 and the final answer must be three digital so the answer is 105.
Here, we discussed how to find the cube roots of exact cube numbers comparing two different
methods. Both scholars have suggested their own method to find the cube roots of non-exact
cubes as well.
1. Jagadguru Swami shree bharati krisna tirthajee Maharaja, Sankaracharya of Govardahana
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1981, 1982
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Impression: 2005
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4. Kumar, Pradeep: Vedic Mathematics, SHREE Book Centre: Reprint 2003, 2004.
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Private limited: 2002, 2003
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Publishers Private limited: First Indian Edition: Delhi, 2002.
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5. 10. Bhaskaracharya, Lilavati, With vasana of Pt. Damodara Mishra, Mithila Institut of Post
Graduate studies and research in Sanskrit Learning Darbhanga: 1959
11. नयराज प"त, प"#डत गेापाल पाडे र उनक$ा घनमूल !याउने रीित, नेपाल राजक%य !"ा !ित$ान, २०३७ िव.सं.
12. भा#कराचाय(, िश#दा&तिशरेामिण, जयदास ह"रदासगु)ः चैाख%बा सं#क%त सी#रज अिफस, िव#ािवलास
!ेस वनारस, 1986
13. गेापाल पाडे, !य#चि&'का, िनण$यसागर, १९४० िव.सं

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