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Prove that: sin780^0sin 120^0+cos 240^0s...

Prove that: `sin780^0sin 120^0+cos 240^0sin390^0=1/2`

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RD SHARMA ENGLISH-TRIGONOMETRIC FUNCTIONS-All Questions
  1. Prove that: t a n 720^0-cos 270^0-sin 150^0cos 120^0=1/4

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  2. Prove that: sin 780^0sin 480^0+cos 120^0sin 150^0=1/2

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  3. Prove that: sin780^0sin 120^0+cos 240^0sin390^0=1/2

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  4. Prove that: sin600^0cos 390^0+cos 480^0sin 150^0=-1

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  5. Prove that : tan 225^@ cot 405^@+ tan 765^@ cot 675^@=0

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  6. Write the maximum and minimum values of cos(cosx)

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  7. Write the maximum and minimum values of sinx dot

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  8. Write the maximum value of sin(cosx)dot

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  9. If sin x=cos^2x ,\ then write the value of cos^2x\ (1+cos^2x)dot

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  10. If sin x+cosec\ x=2, then write the value of sin^n x+cos e c^n xdot

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  11. If sintheta1+sintheta2+sintheta3=3, then costheta1+costheta2+costheta3...

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  12. Write the value of sin 10^0+sin 20^0+sin 30^0+....+sin 360^@

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  13. A circular wire of radius 15cm is cut and bent so as to lie along the ...

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  14. The value for 2(sin^6theta+cos^6theta)-3(sin^4theta+cos^4theta)+1 is

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  15. Write the value of cos1^0+cos2^0+cos3^0++cos 180^0dot

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  16. If cot(alpha+beta)=0\ ,\ then write the value of "sin"(alpha+2beta) .

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  17. If t a n A+cot A=4, then write the value of t a n^4A+cot^4Adot

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  18. Write the least value of cos^2theta+sec^2thetadot

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  19. If x=sin^(14)theta+cos^(20)theta , then write the smallest interval in...

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  20. If 3sintheta+5costheta=5, then write the value of 5sin theta-3costheta...

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