2(x^2+6x+9)+2设t = x+3那么 y = t-6 - √2(t^2+1)所以(y-t+6 )^2 = 2t^2 + 2展开得t^2 - 2(y+6)t + (y+6)^2 = 2t^2 + 2所以t^2 + 2(y+6)t - (y+6)^2 + 2 = 0设y+6 = ut^2 + 2ut -u^2+2=0判别式 = 4*(u^2 + u^2 - 2)...