分类：教育/科学-学习帮助
问题：已知(tan^2)a=2(tan^2)B+1,求证：(sin^2? 
回答：tg^2 A=Sec^2 A-1 Sec^2 A=1/(Cos^2 A)
那么有
Sec^2 A -1 = 2(Sec^2 B -1)+1
Sec^2 A -1 = 2Sec^2 B -1
Sec^2 A =2Sec^2 B
Cos^2 B = 2 Cos^2 A
1-Sin^2 B = 2- 2Sin^2 A
Sin^2B = 2Sin^2 A -1
搞定