Question

已知根号5+1/2=a,求a^5+a^3+a+1/a^6

Answer 1

.

设斜率k

则两条平行线方程：

y=kx ==> kx-y=0

y-3=k(x-1) ==> kx-y+(3-k)=0

根号5=|3-k|/(k^2+1)^(1/2)

5(k^2+1)=(3-k)^2

2k^2+3k-2=0

(2k-1)(k+2)=0

k=1/2或k=-2

所以,两条平行线方程：y=(1/2)x 和y=(1/2)x+(5/2)

或：y=-2x 和y=-2x+5