Question

第三题和第六题怎么做啊

Answer 1

3、(a) 【(x+1)/(x²+2xy+y²)-1/(x²-y²)】(x-y)²/(x²-2y-xy)+(y-x)/(x+y)²
=【(x+1)/(x+y)²-1/(x²-y²)】(x-y)²/(x²-2y-xy)+(y-x)/(x+y)²
=【(x+1)(x-y)-(x+y)】/【(x+y)²(x-y)】(x-y)²/(x²-2y-xy)+(y-x)/(x+y)²
=(x²-xy-2y)/【(x+y)²(x-y)】(x-y)²/(x²-2y-xy)+(y-x)/(x+y)²
=(x-y)/(x+y)²+(y-x)/(x+y)²
=0
(b) 【1+√(a/x) +a/x】x/(√a³-√x³)
=【√(a/x) -1】【1+√(a/x) +a/x】x/【(√a³-√x³)(√(a/x)-1)】
=x【√(a³/x³)-1】/【(√a³-√x³)(√(a/x)-1)】
=(1/√x)/(√(a/x)-1)
=1/(√a-√x)
6、(a)x+4y=1.......①
4x+y=8......②
①*4-②，得 y=-4/15
将y代入①，得 x=31/15
(b) 2x+y²+xy=7.......①
2x+y=1.........②
①-②*y，得 2x-xy=7-y....③
②-③，得 xy=-6
①-②，得 y²-y+xy=6
y²-y-12=0，得y=-3或y=4
当y=-3时，x=2
当y=4时，x=-3/2