①99.8^2②101^2+99^2用完全平方公式解

①99.8^2=(100-0.2)^2=10000-40+0.04=9960.04
②101^2+99^2=(100+1)^2+(100-1)^2=(100^2+1^2)*2=20002

1.(100-0.2)的平方=10000-40+0.04=9960.04
2.（101+99）的平方-2*101*99=40000-19998

1:(100-0.2)^2
=100^2-2*100*0.2+0.2^2
=10000-40+0.04
=9960.04
2:(100+1)^2+(100-1)^2
=10000+2*100*1+1+10000-2*100*1+1
=20002

99.8^2=(100-0.2)^2
=100^2-2*100*0.2+0.2^2
=10000-40+0.04
=19960.04
101^2+99^2=(100+1)^2+(100-1)^2
=100^2+200+1+100^2-200+1
=20000+2
=20002

99.8^2
=(100-0.2)^2
=100^2+0.2^2-2*100*0.2
=10000+0.04-20
=9960.4
101^2+99^2
=(101+99)^2+2*101*99
=20002