Question

求x的平方-y的平方.x+y=5,xy=3

Answer 1

(x-y)^2=(x+y)^2-4xy

=5^2-4×3

=13

∴x-y=±√13

x^2-y^2=(x+y)(x-y)

=5×[±√13]

＝±5√13