Question

x^2+y^2等于什么

顺便解一下x^4+1/x^4
还有^2+1/x^2

Answer 1

x^2+y^2=(x+y)^2-2xy=(x-y)^2+2xy
x^4+1/x^4≥2根号（x^4*（1/x^4））≥2

Answer 2

x^2+y^2=(x+y)^2-2xy

x^4+1/x^4=(x^2+1/x^2)^2-2

x^2+1/x^2=(x+1/x)^2-2