# Find Value of Sin and Cos using Fingers

Today I am going to share with you a special memory trick for trigonometry, mailed to me by Debasis Basak – a young Class IX follower of QuickerMaths.com

By this method we can find out Sines and Cosines of different angles. It just requires your **left hand**. Let’s understand this trick step by step -

**Step 1:- **First mark the angles of 0, 30, 45, 60, and 90 on little, ring, middle and pointer finger and thumb of your left hand.

**Step 2:-**

On the palm of your left hand write the equation √x /2

**Step 3:-**

Suppose, you want to find **Cos30. **

Fold the finger representing 30. i.e. ring finger of your left hand palm. Count the numbers of fingers on the left of the ring finger. So since there are 3 fingers, x=3; put the value in the equation given in step 2

**Step 4:- **Hence,

Cos30 = √3/2

Finding Sine of the same angle is just a simple step away. Of the same left hand, if we count the fingers to the right of the folded finger, we will get value of sine.

Sin30 = √1 /2 = 1/2

Let’s take another example, sin60

60 is represented by pointer finger and there are 3 fingers to the right of this folded finger.

Hence, sin60 = √3/2

I appreciate the efforts of Debasis in sharing this trick with all of us. In case you want to share some quick calculation trick or technique, mail it to me at vineetpatawari [at] gmail [dot] com.

Sir i practice maths regularly bt when i sit for exams nothing works

Hi Krishna,

This is very common. Because of exam stress our mind stops working at optimal level. Meditation at your age might be difficult. Try joggin or some other activity for 30-40 mintues as stress buster during exam days.

Cheers!

Vineet

then what formula should we use for tan ,cot, cosec and sec…

It does not work for SIN 45 or COS 45 .

Hi Ramesh,

The method does work for sin 45 & cos 45 as well. In both hands these ratios are denoted by middle finger. Hence it will be (sq.rt. of 2)/2 = 1/sqrt2

Cheers!

Vineet

Hi friends i found new method by own to calculate square of numbers which ends with 1

For ex. 31

square of 3 is 9 and 2*3 is 6 and square of 1 = 961

similarly 51

square of 5 is 25 and 2*5 is 10,here 1 is passed to previous digit square of 1 = 2601

i have also found for other no. also but again it is bit lengthy.

thanks brother….

it could be simple…..here it goes

angle 0 30 45 60 90

sin sq rt (0/4) sq rt (1/4) sq rt (2/4) sq rt (3/4) sq rt (4/4)

cos (reverse the sequence)

sq rt (4/4) sq rt (3/4) sq rt (2/4) sq rt (1/4) sq rt (0/4)

tan sin 0/cos 0 sin 30/ cos 30…..so on

cosec 1/sin 0 1/sin 30…….so on

sec 1/cos 0 1/cos 30……..so on

cot 1/tan 0 1/tan 30…….so on

That’s really great.

nice idea…. i tried it nd got 2 knw smthng new

Hi Prerna, Let me share something similar on trignometry – very interesting – http://www.quickermaths.com/trigonometry-formula-memorization-trick/

Cheers!

Vineet

how is tan found out and what about sin,how is it found out, is it counting the fingers from your right

Nice article…Keep posting such good article

Its a nice article shared…..Good work…

Certainly a very good Idea; works perfect for at least sine and cosine functions;

However, I didn’t found any glitch in it.

equation is: x=sqrt(x)/2 and not sqrt(x/2).

Perfectly fine for me.

It is certainly a good idea. But there is a small glitch. Sin 30 is 1/2 while Cos 30 is (sqrt 3) /2. The sqrt applies only to 3 and not to 2.

Similarly for 45, both sin and cos is 1 / (sqrt 2).

Needs a bit of tweaking?

no sir , there is no need of tweaking. in sin 30 as you said , when you bend the the ring fnger 30 degrees you know that cos 30 is sqrt 3 /2 for sin please see the fingers lefton the right side . it is 1 therefore sin30 is sqrt1/2 or 1/2

………………..amaxing……………..I appretiate U for making such efforts…………………………

Thankx

can u plz post some more examples how to calculate sin and cos values by fingers?

interesting posts

When you say bend the ring finger the left side has one finger left and on the right side there are 3 fingers. It works for 30 and 90 well but not for all.

Though the efforts are nice

Hello

The formula falls flat when one need to find the value of sin60 and sin 45.

it works man

how it will work plz explain

Excellent!!!

Very educative. Really it is interesting.