Question

递增区间怎么求?函数fx=3-x^2,求f(x^2+4x-5)的递增区间

Answer 1

设t(x)=x^2+4x-5;

f(t)=3-t^2;

则f(x)=3-(x^2+4x-5)^2;

一阶导数f'(x)=-2(x^2+4x-5)(2x+4)=-4(x-1)(x+5)(x+2)

另f‘(x)>0;解得 -2