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sin2(10)sin2(70)sin2(20)+sin2(80)\sin^2(10) - \sin^2(70) - \sin^2(20) + \sin^2(80)

Full solution

Q. sin2(10)sin2(70)sin2(20)+sin2(80)\sin^2(10) - \sin^2(70) - \sin^2(20) + \sin^2(80)
  1. Rewrite using identity: Use the identity sin2(θ)=1cos(2θ)2\sin^2(\theta) = \frac{1 - \cos(2\theta)}{2} to rewrite each term.\newlinesin2(10)=1cos(20)2\sin^2(10) = \frac{1 - \cos(20)}{2}\newlinesin2(70)=1cos(140)2\sin^2(70) = \frac{1 - \cos(140)}{2}\newlinesin2(20)=1cos(40)2\sin^2(20) = \frac{1 - \cos(40)}{2}\newlinesin2(80)=1cos(160)2\sin^2(80) = \frac{1 - \cos(160)}{2}
  2. Substitute into equation: Substitute the expressions back into the original equation.\newline(1cos(20))/2(1cos(140))/2(1cos(40))/2+(1cos(160))/2(1 - \cos(20))/2 - (1 - \cos(140))/2 - (1 - \cos(40))/2 + (1 - \cos(160))/2
  3. Combine like terms: Combine like terms.\newline(121212+12)(cos(20)/2cos(140)/2cos(40)/2+cos(160)/2)(\frac{1}{2} - \frac{1}{2} - \frac{1}{2} + \frac{1}{2}) - (\cos(20)/2 - \cos(140)/2 - \cos(40)/2 + \cos(160)/2)
  4. Simplify constants and cosine terms: Simplify the constant terms and combine the cosine terms. \newline0(cos(20)/2cos(140)/2cos(40)/2+cos(160)/2)0 - (\cos(20)/2 - \cos(140)/2 - \cos(40)/2 + \cos(160)/2)
  5. Use cosine angle sum identities: Use the cosine angle sum identities, cos(180θ)=cos(θ)\cos(180 - \theta) = -\cos(\theta) and cos(θ)=cos(θ)\cos(\theta) = \cos(-\theta), to rewrite cos(140)\cos(140) and cos(160)\cos(160).\newlinecos(20)/2+cos(40)/2cos(20)/2-\cos(20)/2 + \cos(40)/2 - \cos(20)/2
  6. Combine cosine terms: Combine the cosine terms. cos(20)/2cos(20)/2+cos(40)/2-\cos(20)/2 - \cos(20)/2 + \cos(40)/2
  7. Final simplification: Simplify the expression. cos(20)+cos(40)2-\cos(20) + \frac{\cos(40)}{2}

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