cos20/(cos35*√(1-sin20))
分母 = cos35*√(1-sin20) = cos35*(cos10-sin10)
cos35 = cos45cos10 + sin45sin10 = √2/2(cos10+sin10)
所以分母等于√2/2(cos10+sin10)*(cos10-sin10) = √2/2 (cos10^2-sin10^2)= √2/2 cos20
所以结果为 cos20/( √2/2 cos20)= √2