(cos八分之π)的四次方+(sin八分之π)的四次方的值
问题描述：
(cos八分之π)的四次方+(sin八分之π)的四次方的值
答
(cos八分之π)的四次方+(sin八分之π)的四次方
=[cos²π/8+sin²π/8]²-2sin²π/8cos²π/8
=1-1/2(sinπ/4)²
=1-1/2×（√2/2）²
=1-1/4
=3/4