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tAn70Cos10

原式 =cos10(tan60-tan70) =cos10(sin60/cos60-sin70/cos70) =cos10(sin60cos70-sin70cos60)/cos60cos70 =cos10sin(60-70)/(1/2)cos70 =2cos10sin(-10)/sin20 =-2cos10sin10/sin20 =-sin20/sin20 =-1 满意请采纳

cos10/tan20+√3sin10tan70-2cos40 =cos10/cot70+√3sin10tan70-2cos40 =cos10tan70+√3sin10tan70-2cos40 =tan70(cos10+√3sin10)-2cos40 =tan70*2sin(10+30)-2cos40 =2(tan70sin40-cos40) =2(cot20sin40-cos40) =2[(cos20sin40)/sin20-cos40] =2[(...

将tan化成sin/cos的形式 利用倍角公式和和角公式化简 代数式的值=-1 过程如下图:

解:tan70×cos10×(√3tan20-1) =tan70×cos10×(tan60×tan20-1) =tan70×cos10×[(sin60×sin20/cos60×cos20)-1] =tan70×cos10×(sin60×sin20-cos60×cos20)/(cos60×cos20) =tan70×cos10×[-cos(60+20)]/(cos60 ×cos20) =-tan70×cos10×cos80/(cos60×cos20...

tan70×cos10×(-1)(1-√3tan20) =tan70×cos10×(tan60×tan20-1) =tan70×cos10×[(sin60×sin20/cos60×cos20)-1] =tan70×cos10×(sin60×sin20-cos60×cos20)/(cos60×cos20) =tan70×cos10×[-cos(60+20)]/(cos60 ×cos20) =-tan70×cos10×cos80/(cos60×cos...

tan70cos10(√3tan20-1) =tan70*cos10(√3sin20-cos20)/cos20 =2tan70*cos10(√3sin20/2-cos20/2)/cos20 =2tan70*cos10(sin20*cos30...

原式=(sin5/cos5-cos5/sin5)cos70/(1+sin70) =[(sin5)^2-(cos5)^2]/sin5/cos5*cos70/(1+sin70) =-2cos10/sin10*sin20/(1+sin70) =-2cos10/sin10*sin10*cos10/(1+sin70) =-2*(1+cos20)/(1+sin70) =-2

用到公式tanx*tan(90-x)=1 下面证明这个公式 tan(90-x)=sin(90-x)/cos(90-x)=cosx/sinx=1/tanx 公式可以直接用,而且不难记,是吧~ 所以 题目=(tan10*tan80)*(tan20*tan70)*(tan30*tan60)*(tan40*tan50) =1*1*1*1 =1

tansinlim613lim31coslimsinlim222102030...10:设函数f(x)连续,且0)0(f,求极限.)()()(lim000...

原式=[tan(90°-10°)-4cos10°]?3?sin(90°?20°)2?1+cos20°2=(cos10°sin10°-4cos10°)?2(3?cos20°)3?cos20°=2×cos10°?4sin10°cos10°sin10°=2×cos10°?2sin20°sin10°=2×sin80°?sin20°?sin20°sin10°=2×2cos50°sin30°?sin20°sin10°=2×cos50°?sin20°s...

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