问题
选择题
已知f(x)是奇函数,且当x>0时,f(x)=x2-x-1,则当x<0时,f(x)=( )
A.-x2-x+1
B.x2+x-1
C.-x2-x-1
D.x2+x+1
答案
设x<0,则-x>0
∴f(-x)=(-x)2-(-x)-1=x2+x-1
又∵f(x)为奇函数
∴f(x)=-f(-x)=-(x2+x-1)=-x2-x+1
故选:A.
已知f(x)是奇函数,且当x>0时,f(x)=x2-x-1,则当x<0时,f(x)=( )
A.-x2-x+1
B.x2+x-1
C.-x2-x-1
D.x2+x+1
设x<0,则-x>0
∴f(-x)=(-x)2-(-x)-1=x2+x-1
又∵f(x)为奇函数
∴f(x)=-f(-x)=-(x2+x-1)=-x2-x+1
故选:A.
根据所给10个英语单句的意思, 从所给的15个词汇中挑选出10个合适的词或短语填空。
小题1:She told us an ________________story . 小题2:She entered the lab without ______________. 小题3:She is____________________ hearing from her boyfriend in Australia. 小题4:He ______________________________ music. 小题5:They decided to fly to Beijing _________________take a train. 小题6:Whether we’ll go for a picnic __________________ the weather. 小题7:You must ____________ for not being able to meet her on time. 小题8:On the Dragon Boat Festival people usually eat zongzi__________Qu Yuan,a great poet. 小题9:What he said ___________ me _________ my father, he once told me like that 小题10:Farmers have __________ a lot from the new policy(政策). |