贵刊在今年第3期“教学答疑”专栏里刊登了“0.9为什么等于1”一问及解答,解答中用到了高中“等比数列”的知识,这样难度就大了。要想证明0.9=1,方法有多种,除用“等比数列”外还可以用“极限”等知识。在这里向大家介绍另一种简捷证法:用解方程的方法来证明“0.9=1”。证明:设x=0.999……,则10x=9.999……. In the 3rd issue of this year’s “Quality for Teaching” column, you published in the column “0.9 why is equal to 1”. The answer used high school “equivalence series” knowledge, which made it difficult. To prove that 0.9 = 1, there are many ways to use, in addition to “equal ratio series”, you can also use “limit” and other knowledge. Here is another brief introduction to you: Use the solution equation to prove “0.9=1”. Proof: Let x=0.999... then 10x=9.999...