求cos36°sin18°的值

问题描述:

求cos36°sin18°的值

cos36°sin18°=cos36°sin18°cos18° / cos18°利用公式2sina*cosa=sin2a所以sin18°cos18°=0.5sin36°cos36°sin18°cos18°=0.5sin36°cos36°=0.25sin72°于是cos36°sin18°=0.25sin72° / cos18°显然sin72...