1≤x^2+y^2≤,求证0.5≤x^2-xy+y^2≤3

f(x+y)+f(x-y)=2f(x)g(x)求证g(y)≤1 若x.y属于R,且满足（X*X+Y*Y+2）（X*X+Y*Y-1）-18≤0.求证：XY≤2 已知x^2-2xy+y^2+x+y+1=0求证:1/3≤y/x≤3 设x=√（1-y^2）,求证：-1≤x+y≤√2 1≤x^2+y^2≤,求证0.5≤x^2-xy+y^2≤3 已知x²+y²≤1,求证:|x²+2xy-y²|≤根号2 若x.y属于R.且满足(x^2+y^2+2)(x^2+y^2-1)-18≤0.求证:xy≤2 X=Y 求证1=2 已知x,y属于R 满足（x^2+y^+2)(x^2+y^2-1)-18≤0 求证 xy≤2 已知x,y∈R,满足（x²+y²+2)(x²+y²-1)-18≤0.求证：xy≤2 已知非负实数x,y,z满足x+y+z=3 (2),求证x^2/(1+x^4)+y^2/(1+y^4)+z^2/(1+z^4)≤1/(1+x)+1/(1+y)+1/(1+z) 已知x,y,z∈R,若x^4+y^4+z^4=1,求证x^2+y^2+z^2≤根号3 求证：log(2,2^x+2^x²)≥7/8,log(1/2,1/(4^x)+1/(4^x²)≤x+y-1.RT. 设函数f(X)的定义域为R+,且有:1.f(1/2)=1,2.对任意正实数x,y都有f(X*y)=f(x)+f(Y),3.f(x)为减函数(1)求证:当x∈[1,正无穷)时,f(X)≤0(2)求证：当x,y属于R+,都有f（x/y)=f(X)-f(Y)(3)解不等式：f（-x）+f（3-x)≥-2 设函数f(x)的定义域为R,且f(x)不等于0,当x>0,f(x)>1,对x,y属于R,有f(x+y)=f(x)f(y).设函数f(x)的定义域为R,且f(x)不等于0,当x>0时,f(x)>1,对x,y属于R,有f(x+y)=f(x)f(y).（1）求证：f9x)>0（2）解不等式 f(x)≤ 1/f(x+1 用反证法证明:若x+y>2,求证1+x 已知x,y∈R,求证:x^2+y^2≥xy+x+y-1 已知x,y,z∈R,求证:x^2+y^2>=xy+x+y-1