已知tan(π+α)=a²,|cos(π-α)|=-cosα,求1/[cos(π+α)]的值

已知tan(π+α)=a²,|cos(π-α)|=-cosα,求1/[cos(π+α)]的值
已知tan(π+α)=a²,|cos(π-α)|=-cosα,求1/[cos(π+α)]的值

已知tan(π+α)=a²,|cos(π-α)|=-cosα,求1/[cos(π+α)]的值
|cos(π-α)|=-cosα>0
所以cos(π+α)=-cosα>0
tan(π+α)=a²=sin(π+α)/cos(π+α)>=0
所以sin(π+α)0
因此 1/[cos(π+α)]=(1+a^4)^(1/2)