求证:(1-cosa的4次方-sina的4次方)/(1-cosa的6次方-sina的6次方)=2/311
问题描述:
求证:(1-cosa的4次方-sina的4次方)/(1-cosa的6次方-sina的6次方)=2/3
11
答
(1-cos^4a-sin^4a)/(1-cos^6a-sin^6a)=[1-(cos^4a+sin^4a+2cos^2asin^2a)+2cos^2asin^2a]/[1-((cos^2a)^3+(sin^2a)^3)]=[1-(cos^2a+sin^2a)^2+2cos^2asin^2a]/[1-(cos^2a+sin^2a)(cos^4a+sin^4a-...