Finding Square of an adjacent number

Finding Square of an adjacent number: One up

You know the squares of 30, 40, 50, 60 etc. but if you are required to calculate square of 31 or say 61 then you will scribble on paper and try to answer the question. Can it be done mentally? Some of you will say may be and some of you will say may not be. But if I give you a formula then all of you will say, yes! it can be. What is that formula…..

The formula is simple and the application is simpler.

Say you know 60² = 3600

Then 61² will be given by the following

61² = 60² + (60 + 61) = 3600 + 121 = 3721

or Say you know 25² = 625 then

26² = 625 + (25 + 26) = 676

Like above, you can find out square of a number that is one less than the number whose square is known.


 Finding Square of an adjacent number: One Below

You know the squares of 30, 40, 50, 60 etc. but if you are required to calculate square of 29 or say 59 then you will scribble on paper and try to answer the question. Can it be done mentally? Some of you will say may be and some of you will say may not be. But if I give you a formula then all of you will say, yes! it can be. What is that formula…..

The formula is simple and the application is simpler.

Say you know 60² = 3600

Then 59² will be given by the following

59² = 60² - (59 + 60) = 3600 - 119 = 3481

or Say you know 25² = 625 then

24² = 625 - (24 + 25) = 625 - 49 =  576

Like above, you can find out square of a number that is one less than the number whose square is known.