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 -
First mark the angles of 0, 30, 45, 60, and 90 on little, ring, middle and pointer finger and thumb of your left hand.
On the palm of your left hand write the equation √x /2
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
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.