若x+y=4,xy=3,分别求下列各式的值：(1)1/x+1/y(2)1/x^2+1/y^2

Question

若x+y=4,xy=3,分别求下列各式的值：(1)1/x+1/y (2)1/x^2+1/y^2

Answer 1

(1)1/x+1/y
=xy/(x+y)
=3/4
(2)1/x^2+1/y^2
=(1/x+1/y)^2-2/xy
=9/16-2/3
=-5/48