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In any quadrilateral ABCD, show that : ...

In any quadrilateral ABCD, show that :
`cos A cos B - cos C cos D = sin A sin B-sin C sin D`.

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MODERN PUBLICATION-TRIGNOMETRY-EXERCISE
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  3. In any quadrilateral ABCD, show that : cos A cos B - cos C cos D = si...

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  4. Prove that : cos theta- sin theta= sqrt2 cos (theta+ pi/4).

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  8. Find a and b such that a le3 cos theta +5 sin (theta-pi/6)le b holds ...

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  9. If sin alpha=15/17 and cos beta=12/13, find the values of : sin (alpha...

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  10. If sin alpha=15/17 and cos beta=12/13, find the values of : cos (alph...

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  11. If sin alpha=15/17 and cos beta=12/13, find the values of : tan (alph...

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  12. If cos (alpha+beta)=4/5, sin (alpha -beta)=5/13 and alpha, beta lie b...

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  13. Find the value of tan (alpha+beta), given that : cot alpha=1/2, alpha...

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  14. If theta+phi= alpha and tan theta=k tan phi, prove that : sin alpha=(...

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  15. Prove the following: cos((3pi)/4+x)-cos((3pi)/4-x)=-sqrt2 sinx

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  16. Prove that cos((pi)/(4)+x)+cos((pi)/(4)-x)=sqrt(2)cosx

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  17. Prove the following : (sin 5x + sin3x)/(cos 5x + cos 3x)= tan 4x.

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  18. Prove the following : (sinx +siny)/(cos x+cos y)= tan frac (x+y)(2).

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  19. Prove the following : (sinx +sin3x)/(cos x + cos 3x)= tan 2x.

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  20. Prove the following: (sin x-sin y)/(cosx + cos y)=tanfrac(x-y)(2)

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