(1)令x²+y²=t,则原方程化为:8t²-t=1,解得:t1=(1+根号33)/16,t2=(1-根号33)/16,
即:x²+y²=(1+根号33)/16或x²+y²=(1-根号33)/16
(2))(x-3)(x-4)(x-5)=(x-4)(x-5)(x-6)(x-7),若x=4或x=5时,原等式成立,故x1=4,x2=5,若x≠4或x≠5,原方程化简为:x-3=(x-6)(x-7),解得:x3=9,x4=5,综上:原方程的解为:x1=4,x2=5,x3=9
(3)不是方程,或题目有误,请你改正我后再解.