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Math

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Use a counter example to show that cos(x+y)= cosx +cosy is not an identity

  • Math - ,

    Let x=π/4, y=π/4,
    cos(x+y)
    =cos(π/4+π/4)
    =cos(π/2)
    =0
    cos(x)+cos(y)
    =cos(π/4)+cos(π/4)
    =√2/2+√2/2
    =√2
    Since √2 ≠ 0,
    cos(x+y) ≠ cosx +cosy

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