因为x∈[π/6,2π/3],所以π/24≤x-π/8≤13π/24,显然13π/24大于π/2,所以最小值cos13π/24=cos(2π/3-π/8)=cos2π/3cosπ/8+sin2π/3sinπ/8,
cosπ/8和sinπ/8,利用半角公式可以算出.
因为x∈[π/6,2π/3],所以π/24≤x-π/8≤13π/24,显然13π/24大于π/2,所以最小值cos13π/24=cos(2π/3-π/8)=cos2π/3cosπ/8+sin2π/3sinπ/8,
cosπ/8和sinπ/8,利用半角公式可以算出.