sin71°cos64°+sin19°sin64°的值为

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sin71°cos64°+sin19°sin64°的值为

sin71°cos64°+sin19°sin64°
=cos19°cos64°+sin19°sin64°
=cos(19°-64°)
=cos(-45°)
=cos45°
=√2/2

1/2(sin135 + sin 7) + 1/2(cos 45 -cos 83 )=0