## Hello Friends

## welcome to this post of learning trigonometric formulas with me .Most of the Students or Mathematics Learner ,most of the time confuse to remember or memorise A B and C D formulas,They mixed A B and C D formulas with each other and could not reproduce what they have learnt . So today we going to learn new techniques to learn "How to memorise AB and CD formulas" forever. Before this we must have knowledge of different trigonometric values of different angles in different quadrants.

First of all have a quick look at some of these formulas .

To clear your all doubts on " How to Calculate Different Trigonometric values in different quadrants " in an easy Method. click on the above links .

## Tricks to Learn A B Formulae For sine angles

When angles are added i. e
**
Sin ( A+B )
**

When Angles are added and then their Trigonometric Ratios is taken , and if we have to take the Sine of added angles, then it can be done like this.

Start with sine of angle A and multiply it with cosine of angle B and in other part i. e. After +ve sign Start with Cosine of angle A and multiply with Sine of angle B. i.e. start with sine and ends with sine and in middle both the terms are cosine ,and angles start A then B again A then again B.

##
**
Sin (A+B) = Sin A Cos B + Cos A Sin B
**

When angles are subtracted i. e
**
Sin ( A-B )
**

**
**

When Angles are subtracted and their Trigonometric Ratios is taken , and if we have to take the Sine of subtracted angles, then it can be done like this

Start with sine of angle A and multiply it with cosine of angle B and in other part i. e. After
**
+ve sign
**
Start with Cosine of angle A and multiply with Sine of angle B. i.e start with sine and ends with sine and in middle both the terms are cosine ,and angles start with A then B again A then again B.

##
**
Sin (A - B) = Sin A Cos B - Cos A Sin B
**

## Tricks to Learn A B Formulae For Cosine angles

When angles are added i. e
**
Cos ( A+B )
**

**
**

When Angles are added and then their Trigonometric Ratios is taken , and if we have to take the Cosine of added angles, then it can be done like this.

Start with cosine of angle A and multiply it with cosine of angle B and in other part i. e. After
**
-ve sign
**
**
**
Start with Sine of angle A and multiply with Sine of angle B. i.e. 1
^{
st
}
and 2
^{
nd
}
terms are cosine and 3
^{
rd
}
and 4
^{
th
}
terms are sine , Angles start with A then B again A then again B.

"Here Sum of cosine of Two angles is equal to difference of product of cosines of both the angles and product of sine of both the angles ".

##
**
Cos (A+B) = Cos A Cos B - Sin A Sin B
**

When angles are subtracted i. e
**
**
**
Cos ( A-B )
**
**
**

When Angles are subtracted and then their Trigonometric Ratios is taken , and if we have to take the cosine of subtracted angles, then it can be done like this.

##
**
Cos (A - B) = Cos A Cos B + Sin A Sin B
**

Start with cosine of angle A and multiply it with cosine of angle B and in other part i. e. After
**
+ve sign
**
Start with Sine of angle A and multiply with Sine of angle B. i. 1
^{
st
}
and 2
^{
nd
}
terms are cosine and 3
^{
rd
}
and 4
^{
th
}
terms are sine , and angles start with A then B again A then again B.

"Here Difference of cosine of Two angles is equal to the Sum of product of cosines of both the angles and product of sine of both the angles" .

**
Want to Learn
WHAT IS SET, TYPES OF SETS ,UNION ,INTERSECTION AND VENN DIAGRAMS
.
**

##
**
How to Memorise C D Formulae
**

## To learn C D formulae

## Step 1

## Place 2 for all four formulae and take Trigonometric Ratio of 1st angle for all four formulae which is (C+D)/2 and again trigonometric Ratio of 2nd angle which is (C-D)/2.

## Step 2.1

## For addition of Sine Formula start with sine of 1st angle as mentioned in step 1 and multiply it with cos of 2nd angle as mentioned in step 1.

## Step 2.2

For subtraction of Sine Formula start with cosine of 1st angle as mentioned in step 1 and multiply it with sine of 2nd angle as mentioned in step 1.

**
Step 3.1
**

## For addition of cosine Formula start with cosine of 1st angle as mentioned in step 1 and multiply it with cosine of 2nd angle as mentioned in step 1.

**
Step 3.2
**

## For subtraction of cosine Formula start with sine of 1st angle as mentioned in step 1 and multiply it with sine of 2nd angle as mentioned in step 1,and do not forget to multiply it with -ve sign.

**
or
**

If you do not want to multiply it with -ve sign ,then you can change 2nd angle (D-C)/2 instead of (C-D)/2

How to Memorise A B and C D formulas easily ,watch this video

**
Want to learn
MATRIX , DIFFERENT TYPES OF MATRICES AND DETERMINANTS
.
Want to learn
HOW TO SOLVE LINEAR EQUATIONS OF TWO AND THREE VARIABLES || MATRIX METHOD TO SOLVE SYSTEM LINEAR EQUATIONS
.
**

## Conclusion

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