因式分2x^2+3xy-2y^2+7x-3y+3=(2x-y+1)(x+2y-3)
化简求值：由题锝a^2=3a-1
则原式=(a^2(2a^3-5a^2+2a-8))/(a^2+1)
=((3a-1)(2a(3a-1)-5(3a-1)+2a-8))/((3a-1)+1)
=((3a-1)(6a^2-15a-3))/(3a)
=((3a-1)(6(3a-1)-15a-3))/(3a)
=((3a-1)(3a-9))/(3a)
=(3a^2-10a+3)/a
=(3(3a-1)-10a+3)/a
=(-a)/a
=-1
计算：（1）由于1/p+1/q=1/(p+q)
则(p+q)/p+(p+q)/q=1
则2+p/q+q/p=1
则p/q+q/p=-1
(2)由于1/p-1/q=1/(p+q)
则(p+q)/p-(p+q)/q=1
则p/q-q/p=1
则(p/q-q/p)^2=(p/q)^2-2+(q/p)^2=1
则(p/q)^2+2+(q/p)^2=5
则(p/q+q/p)^2=5
则p/q+q/p=正根号5或负根号5
(3)由题可设x/(a-b)=y/(b-c)=z/(c-a)=t
则x+y+z=t(a-b)+t(b-c)+t(c-a)
=0
(4)由题可得x=4z,y=3z
则原式=(16+9+1)/(2*16+9-1)=13/20