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
Finding Square of an adjacent number: One below
Likewise, you can find out square of a number that is one less than the number whose square is known.
Let me show it by taking an example:
Say you know 602 = 3600
Then 592 will be given by the following
592 = 602 – (60 + 59) = 3600 – 119 = 3481
or Say you know 252 = 625 then
242 = 625 – (25 + 24) = 576
Apply it to find square of a digit, which is one, less than the square of known digit. This works very well for the complete range of numbers.
Finding Square of a number ending with 5
After learning this you will be able to find square of a number ending with 5 say 25, 35, 45 etc. You can even try to find square of a three digit number ending with 5 say 105, 115, 125 etc.
Say you want to find square of 85
Do the following:
· Multiply 5 by 5 and put 25 as your right part of the answer.
· Multiply 8 by the next higher digit i.e 9 and put 72 as your left part of the answer.
· Your answer is 7225
You can use this formula to find square of any number ending with 5.
More details can be found at Magical Methods