38.9^2-77.8*48.9+48.9^2补充:(a+2b)(a-2b)-1/2b(a-8b)

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38.9^2-77.8*48.9+48.9^2补充:(a+2b)(a-2b)-1/2b(a-8b)38.9^2-77.8*48.9+48.9^2补充:(a+2b)(a-2b)-1/2b(a-8b)38

38.9^2-77.8*48.9+48.9^2补充:(a+2b)(a-2b)-1/2b(a-8b)
38.9^2-77.8*48.9+48.9^2
补充:(a+2b)(a-2b)-1/2b(a-8b)

38.9^2-77.8*48.9+48.9^2补充:(a+2b)(a-2b)-1/2b(a-8b)
哈,这个简单!
原式=(38.9-48.9)^2
=100

38.9^2-77.8*48.9+48.9^2
=38.9^2-2*38.9*48.9+48.9^2
=(38.9-48.9)^2
=(-10)^2
=100

不懂可追问,有帮助请采纳,谢谢!

38.9^2-77.8*48.9+48.9^2
=38.9^2-2*38.9*48.9+48.9^2
=(48.9-38.9)^2
=10^2
=100
希望采纳!
:(a+2b)(a-2b)-1/2b(a-8b)
=a^2-4b^2-1/2ab+4b^2=a^2-1/2ab

38.9^2-77.8*48.9+48.9^2=38.9^2-2*38.9*48.9+48.9^2=(38.9-48.9)^2=10^2=100

a^2-2ab+b^2 = (a-b)^2

初中平方差公式没学好吧,绝对的!