设4X²+y²+4X-8Y+17=0 求X+y的值
问题描述:
设4X²+y²+4X-8Y+17=0 求X+y的值
答
4X²+y²+4X-8Y+17=0 ﹙4x²+4x+1﹚+﹙y²-8y+16﹚=0﹙2x+1﹚²+﹙y-4﹚²=0∵ ﹙2x+1﹚²≥0,﹙y-4﹚²≥0∴ 2x+1=0,x=﹣1/2y-4=0,y=4∴ x+y=﹣1/2+4=7/2....