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Show that (cos^(2)theta - sin^(2)theta...

Show that
`(cos^(2)theta - sin^(2)theta)=(2tan theta)/((1- tan^(2)theta)) ` is not an identity .

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Verified by Experts

Putting ` theta = 30^(@), ` we find :
` LHS = (cos^(2)30^(@)- sin^(2)30^(@)) `
`={((sqrt(3))/(2))^(2)-((1)/(2))^(2)}=((3)/(4) - (1)/(4)) = (2)/(4)=(1)/(2), and `
` RHS = (2 tan 30^(@))/((1- tan^(2)30^(@)))=(2 xx (1)/(sqrt(3)))/([1-((1)/(sqrt(3)))^(2)])=((2)/(sqrt(3)))/((1- (1)/(3)))=((2)/(sqrt(3)) xx (3)/(2)) = sqrt(3). `
` therefore LHS ne RHS. `
Hence, the given equation is not an identity.
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RS AGGARWAL-TRIGONOMETRIC IDENTITIES-Test Yourself
  1. Show that (cos^(2)theta - sin^(2)theta)=(2tan theta)/((1- tan^(2)the...

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  2. (cos^(2)56^(@)+cos^(2)34^(@))/(sin^(@)56^(@)+sin^(2)34^(@))+3tan^(2)56...

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  3. (sin^2 30^@ cos^2 45^@+4 tan^2 30^@+1/2 sin^2 90^@+1/8 cot^2 60^@)=?

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  4. If cosA+cos^(2)A=1, then sin^(2)A+sin^(4)A=?.

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  5. If sin theta=(sqrt(3))/(2)" then " ("cosec"theta+cot theta)=?

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  6. If cotA=(4)/(5), then ((sinA+cosA))/((sinA-cosA))=?

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  7. If 2x=secA and (2)/(x)=tanA, " prove that " (x^(2)-(1)/(x^(2)))=(1)/(4...

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  8. If sqrt(3) tantheta=3sintheta, " prove that " (sin^(2)theta-cos^(2)the...

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  9. Prove that ((sin^(2)73^(@)+sin^(2)17^(@)))/((cos^(2)28^(@)+cos^(2)62^(...

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  10. If 2sin2 theta=sqrt(3) ,then the value of theta is :

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  11. Prove that sqrt((1+cosA)/(1-cosA))=("cosec"A+cotA).

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  12. If cosec theta + cot theta= p, cos theta = ?

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  13. Prove that ("cosec"A-cotA)^(2)=((1-cosA))/((1+cosA)).

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  14. If 5cottheta=3. find the value of (5sintheta-3costheta)/(4sintheta+3co...

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  15. Prove that (sin32^(@)cos58^(@)+cos32^(@)sin58^(@))=1.

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  16. If x=a sin theta+b cos theta and y=a cos theta -b sin theta, " prove t...

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  17. ((1+sintheta))/((1-sintheta))=?

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  18. Prove that (1)/((sec theta - tan theta))-(1)/(cos theta)=(1)/(cos th...

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  19. ((sinA-2sin^(3)A))/((2cos^(3)A-cosA)) = ?

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  20. Prove that (tanA)/((1-cotA))+(cotA)/((1-tanA))=(1+tanA+cotA).

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  21. If sec5A="cosec"(A-36^(@)) and 5A " is an acute angle, show that " A=2...

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