sin10°乘以sin40°+sin50°乘以sin80°

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sin10°乘以sin40°+sin50°乘以sin80°sin10°乘以sin40°+sin50°乘以sin80°sin10°乘以sin40°+sin50°乘以sin80°原式=cos80°cos5

sin10°乘以sin40°+sin50°乘以sin80°
sin10°乘以sin40°+sin50°乘以sin80°

sin10°乘以sin40°+sin50°乘以sin80°
原式=cos80°cos50°+sin50°sin80°
=cos(80°-50°)
=cos30°
=(根号3)/2