కింది వాటిని మూల్యాంకనం చేయండి:

cos(36° + A).cos(36° - A) + cos(54° + A).cos(54° - A)

This question was previously asked in
SSC CGL 2023 Tier-I Official Paper (Held On: 14 Jul 2023 Shift 2)
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  1. sin 2A
  2. cos A
  3. sin A
  4. 2A

Answer (Detailed Solution Below)

Option 4 : 2A
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SSC CGL Tier 1 2025 Full Test - 01
100 Qs. 200 Marks 60 Mins

Detailed Solution

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ఇచ్చిన దత్తాంశం:  

cos (36° - A) cos (36° + A) + cos (54° - A) cos (54° + A)

ఉపయోగించిన సూత్రం: 

cos (a - b) = cos a cos b + sin a sin b.

sin (90 - a) = cos a

సాధన:            

⇒ sin[90 - (36 - A)]sin[90 - (36 + A)] + cos (54° - A) cos (54° + A)

⇒ sin(54 º + A)sin(54 º - A) + cos (54° - A)cos (54° + A)

⇒ గుర్తింపు cos (A - B)ని ఉపయోగించడం

⇒ cos(54 + A - 54 + A) = cos(2A)

కాబట్టి, cos (36° - A) cos (36° + A) + cos (54° - A) cos (54° + A) విలువ cos(2A).

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