已知x>y,求证x³-y³>2x²y-2xy²
题目
已知x>y,求证x³-y³>2x²y-2xy²
答案
x³-y³-(2x²y-2xy²)=x³-y³-2xy(x-y)=(x-y)(x^2+xy+y^2)-2xy(x-y)=(x-y)(x^2-xy+y^2)x>y>=0,(x-y)(x^2-xy+y^2)=(x-y)[x(x-y)+y^2)]>0x>=0>y,(x-y)(x^2-xy+y^2)=(x-y)[x^2+x(-y)+y^2)]>0...
举一反三
已知函数f(x)=x,g(x)=alnx,a∈R.若曲线y=f(x)与曲线y=g(x)相交,且在交点处有相同的切线,求a的值和该切线方程.
我想写一篇关于奥巴马的演讲的文章,写哪一篇好呢?为什么好
最新试题
热门考点