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Hot goIITian

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4 Aug 2010 19:10:47 IST

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For questions of the form sin^2a-sin^2b can i directly use the formula of sin(a+b)sin(a-b) in the sc

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For questions of the form sin^2a-sin^2b can i directly use the formula of sin(a+b)sin(a-b) in the school examinations. What's the formula for cos^2a-cos^2b.

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silent killer

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4 Aug 2010 19:30:13 IST

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SAME THING...COS(2A+2B)COS(2A-2B)

Astha Sharma

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4 Aug 2010 20:05:14 IST

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No, you can't use that formula or I should say there is no such formula.

The formula is (sin a+ sin b)(sin a - sin b) for (sin^2 a - sin^2 b) ----{the basic formula used is (a^2-b^2)=(a+b)(a-b) }

Similarly for cos, you can use it.

ASTGS

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4 Aug 2010 21:30:52 IST

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they both do exist(Refer to NCERT text book ex3.4 q no. 12 and q no.13 ). Prove cos^2(2x)-cos^(6x)=sin 4xsin8x

Astha Sharma

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5 Aug 2010 19:16:37 IST

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We cannot call it a general formula since it doesn't follow the same pattern for cosine function. See the last question you have typed. And every question cannot be a formula .Do you think you have to learn every question in the form of a formula? (then I would be lost if I learn 25 questions of the ex you've mentioned)

Inferno

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6 Aug 2010 19:01:55 IST

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The formulae exist. It's true did you not study them.

ASTGS

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6 Aug 2010 19:06:08 IST

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The questions i have mentioned are just to show the application of the formulae. They are both genuine formulae and who said that every question is a different formula. I think you got me wrong.

silent killer

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6 Aug 2010 19:33:04 IST

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this formula do exist...i have seen it.if u still dont believr,just type it in google and see it....thats all i can say.

ASTGS

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7 Aug 2010 07:44:11 IST

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Did I say that those two formulae do not exist. If so then that's my mistake. Pardon me. But I don't think that I said so.

And I am still waiting for the reply to the first part of my question, The formulae which I did quote in the question, are mentioned no where in the textbook. So can I apply it directly in the school examinations.

silent killer

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8 Aug 2010 21:40:26 IST

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MR AGTS,HAVE I MENTIONED U SAID TAT. I TOLD IT TO ASTHA SHARMA....I F U DID NOT SAY TAT,THEN Y SHUD I SAY IT TO U?

lata

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8 Aug 2010 23:10:03 IST

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THE ANSER IS SIN(A+B)SIN(B-A) THATS IT . WATS THE FIGHT FOR????????????

silent killer

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9 Aug 2010 05:23:58 IST

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ok,@AGTS,u shud not use these formulas in ncert exam,bcz they always expect formulas(given directly in ncert and not the derived ones from solved examples)....if it is one mark or two merk ,they only expect the answer to be written.there u can use it.but if it is a 3 or 4 marks,they will ask the steps and u are gone.....so strictly stick on to the formulas of ncert to get high scores in the exam.......

ASTGS

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10 Aug 2010 18:59:15 IST

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I am sorry if my last reply appeared rude to you. Thanks for the help.

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