How to remember trigonometry product to sum formula and sum to product formula

In this video explaining trigonometry standard formula. Using these formula solve the problems.

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Please watch: "Simple and easily explain basic properties Scalar product important rules"
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[王万霖]

It's really helpful, I could only memorize angle sum and difference identities then I could get these formulas!

[Kat-ibyt]

Now that the logic is clear its easy to learn Thank you!!!

[ayushaggarwal]

Aree derivation toh sabko pata hai but trick chaiye thi Taki her baar derive naa Karna pade
Video title me derivation likhna tha naa

[keshavmaheshwari]

Thank you thank you thank you thank you more time thank you sir

[agentgamer]

Really helped me a lot … jazakallah sir