Question

x的平方+y的平方=12,求xy的值

Answer 1

1.已知x^2+y^2=12,x+y=4.求xy的值.

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

16=12+2xy

2xy=4

xy=2

2.99乘101乘10001

=(100-1)(100+1)10001

=(100^2-1)(100^2+1)

=100^4-1

=99999999