51^2-51x98+49^2=51^2-51*2*49+49^2
=51^2-51*49+49^2-51*49
=51*(51-49)-(51*49-49^2)
=51*2-49(51-49)
=(51-49)*2
=4
学了完全平方式,直接用就是(51-49)^2
完全平方公式
x^2-2XY-Y^2=(X-Y)^2
51^2-51x98+49^2
=51^2-2x51x49+49^2
=(51-49)^2
=4
解:51^2-51*98+49^2=51^2-2*51*49+49^2=(51-49)^2=2^2=4
设51=a 49=b 则a^2-2ab+b^2=(a-b)^2=(51-49)^2=2*2=4
51^2-2*51*49+49^2=(51-49)^2=2^2=4