cos8分之兀的導數等於cos(π/8)=√((1+cosπ/4)/2)=√((1+√2/2)/2

解法如下

=1/2×√(2+√2)cos(π/8)=√((1+cosπ/4)/2)

=√((1+√2/2)/2)

=1/2×√(2+√2)cos(π/8)=√((1+cosπ/4)/2)

=√((1+√2/2)/2)

=1/2×√(2+√2)cos(π/8)=√((1+cosπ/4)/2)

=√((1+√2/2)/2)

=1/2×√(2+√2)cos(π/8)=√((1+cosπ/4)/2)

=√((1+√2/2)/2)

=1/2×√(2+√2)cos(π/8)=√((1+cosπ/4)/2)

=√((1+√2/2)/2)

=1/2×√(2+√2)

cos三分之π是某個數字常數，而常數的導數是0y=cosπx/3 y'=-(π/3)•sinπx/3

y=cosπ/6=cos30°=√3/2是一個定值，即為常數，根據常數的導數為0，得到y=cosπ/6的導數=0.

y=cos(π/6)=√3/2

y'=0

常函式的導數是0

cos(二分之π+三分之π)

=-cos(3分之π)

=-1/2

你的題目應該寫錯了，函數里面都沒有x

此外

cos(二分之π+三分之π)

=-cos(3分之π)

=-1/2