Question

The value of cos65° cos55 cos5° must be​

Answer 1

Answer:

Remember ,

cos@*cos(60-@)*cos(60+@) = 1/4[cos3@]

so,

cos5°*cos55°*cos65° = 1/4[cos15°] = 1/4[ (√3 + 1 )/2√2]

= (√3 + 1 )/8√2 (Ans.)

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