cos2o=2(coso)^2-1=2(3/5)^2-1=-7/25
不等。理解定义，最方便的办法是画图：sin=对/斜，cos=邻/斜、20°的邻边大于对边 cos（-20°）画图，邻边在x轴正方向，对边在y轴负方向，最终取值是负值。所以没学明白的，最节省时间和精力的办法，就是画图。一目了然。熟能生巧，等到看题自然能在脑海里画图的阶段，就巩固了。
2cos2o【题目】 证明:coso=sin2a sino 相关知识点: 试题来源: 解析 【解析】证明: 2cos2a 2cos2os ∵左边 COSO -tana 2cos2asinacosa =(cos2αsin2α)/(cos^2α)=sin2α= 右边 , 即左边=右边, ∴ 证等式成立, 2cos2o 综上所述,结论是: coso -tana sino ...
Biomass burning as a source of atmospheric gases CO, H2, N2O, NO, CH3Cl and COS Biomass burning can contribute extensively to the budgets of several gases which are important in atmospheric chemistry. In several cases the emission is comparable to the technological source. Most burning takes pl...
将括号打开，整理得1/2（cos-sin）（cos sin），也就是1/2（cos^2-sin^2），得1/2cos20=1/8，到这就懂了吧
=cos(2o)cos(3π/5)+sin(2o)sin(3π/5)=0+4/9sin(3π/5)=4/9sin(3π/5)=4/9*(-1+√5)/4 =(-1+√5)/9 sin(3π/5)=sin108°=sin(90°+18°)=cos18° cos54°=sin36° 4cos³18°-3cos18°=2sin18°cos18° 同除以cos18° 4cos²18°-3=2sin18...
2.2. Preparation of CoS-Co2O3/G-C3N4 Nanocomposite First, 10 g of urea was well annealed in a tube furnace at 550 °C for 2 h under an N2atmosphere. This led to the combustion and conversion of urea to G-C3N4. For the preparation of the composite, (0.1 M) Co(CH3COOH)2, (0.2 ...
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百度试题 结果1 题目(2分) cos30o=( ) 相关知识点: 试题来源: 解析 C 反馈 收藏
百度试题 结果1 题目T_1+cos_2oo_3+5a_2+C_2C_2+H_2O+CO_2↑.CaOHSO_4 相关知识点: 试题来源: 解析 A 反馈 收藏