已知：ax+by=7 ax2+by2=49 ax3+by3=133 ax4+by4=406 求1995(x+y)+6xy-17(a+b)/2
2019-12-16
已知：ax+by=7 ax2+by2=49 ax3+by3=133 ax4+by4=406 求1995(x+y)+6xy-17(a+b)/2
优质解答
∵ ax2=x(7-by), by2=y(7-ax)相加：49=ax2+by2= 7x-bxy＋7y-axy＝7(x+y)-xy(a+b) ①又：ax3=49x-bxy2, by3=49y-ax2y相加得 133=ax3+by3=49(x+y)-xy(ax+by)即 49(x+y)-7xy=133 , 7(x+y)-xy=19 ②同理 ax4=133x...
∵ ax2=x(7-by), by2=y(7-ax)相加：49=ax2+by2= 7x-bxy＋7y-axy＝7(x+y)-xy(a+b) ①又：ax3=49x-bxy2, by3=49y-ax2y相加得 133=ax3+by3=49(x+y)-xy(ax+by)即 49(x+y)-7xy=133 , 7(x+y)-xy=19 ②同理 ax4=133x...