0.98x1.02＝（1-0.02）x（1+0.02）＝1²-0.02²＝1-0.0004＝0.9996
＝0.98x（1+0.02）＝0.98+0.0196＝0.9996
=(1-0.02)×(1+0.02)=1-0.0004=0.9996
