已知y=2x,则4x2-y2的值是______.
已知x2+4x+y2-2y+5=0,则x2+y2=______.
已知:x+y=4,x2-y2=20,则x-y的值是______.
(选做题)已知x+2y=1,则x2+y2的最小值是______.
已知实数x、y满足(x2+y2)(x2+y2-1)=2,则x2+y2的值为______.
已知x、y是实数且满足x2+xy+y2-2=0,设M=x2-xy+y2,则M的取值范围是______.
已知实数x,y满足x2+y2=2x,则x2y2的取值范围是______.
已知x-y=2,则x2-y2-4y=______.
已知x-y=5,(x+y)2=49,则x2+y2的值等于______.
已知实数x,y满足x2+y2-2x+4y=0,则x2+y2的最小值是
已知实数x、y满足x2+4xy+4y2+x+2y-6=0,则x+2y的值为______.
已知x2-4y2=20,x+2y=5,则x=______,y=______.
已知x+y=4,xy=2,则x2+y2+3xy=______.