高一数学必修4题目

显示全部楼层 · 2011-1-25 18:36:32

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×sin10/(cos60×cos20) =-(sin70/cos70)×(1/2)×sin20/(cos60×cos20) =-(cos20/sin2...

千问 · 2011-1-25 18:36:32

=cos10°（根号3·tan70°·tan20°—tan70°）=cos10°（根号3—tan70°）=cos10°（tan60°—tan70°）=cos10°· tan(60°-70°)·(1+tan60°·tan70°)=cos10°· tan(-10°)·(1+tan60°·tan70°)=-sin10°·(cos60°·cos7...

千问 · 2011-1-25 18:36:32

原式=sin70°／cos70°×cos10°×(√3×sin20／cos20－1)
=cos20°/sin20°×cos10°×(√3×sin20／cos20－1)
=cos20°／2sin10°×(√3×sin20／cos20－1)
=√3×sin20°／2sin10°－cos20°／2sin10°...