The diameter of a certain pollen grain is 25 microns by scientific counting method, and how many pollen grains can be arranged up to 1m in sequence (1um = 10 ^ - 3mm = 10 ^ - 6m) Factorization of (x ^ 2-xy) ^ 2 - (xy-y ^ 2) ^ 2

The diameter of a certain pollen grain is 25 microns by scientific counting method, and how many pollen grains can be arranged up to 1m in sequence (1um = 10 ^ - 3mm = 10 ^ - 6m) Factorization of (x ^ 2-xy) ^ 2 - (xy-y ^ 2) ^ 2

1.40000 (1000000 μ m △ 25 μ m)
2. Final answer (X & # 178; - Y & # 178;) &# 178; (if necessary, continue to ask

Jinan's planned annual output of iron and steel in the eleventh five year plan is 15 million tons, which is expressed by scientific notation ()
A. 1.5 × 106 tons B. 0.15 × 108 tons C. 1.5 × 107 tons D. 0.15 × 107 tons

15 million = 15 million = 1.5 × 10, so C

Prove that 12 / 99 is equal to 0.12

Let 0.121212. = X,
There are 100x = 12.121212
By subtracting the two formulas, we get 99x = 12
X = 12 / 99, i.e. 12 / 99 = 0.121212

How much is 99 * 25.12 + 25.12

99×25.12+25.12
=（99+1）×25.12
=100×25.12
=2512

90 divided by 15 is equal to 90

90 divided by 15 = 15 divided by 90
15÷90=1/6
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15 square equals 10x

X^2+15=10X
X^2-10X+25-10=0
(X-5)^2=10
Then x = 5 + radical 10, or x = 5 - radical 10

(- 1 by 2) + (- 1 / 2 by 3) + ····· + (- 1 / 2010 by 1 / 2011) is equal to

Knowledge point: 1 / N (n + 1) = 1 / n-1 / (n + 1)
The original formula = - (1-1 / 2 + 1 / 2-1 / 3 + 1 / 3-1 / 4 +...) +1/2010-1/2011)
=-(1-1/2011)
=-2010/2011

The last digit of 1 ^ 2 + 2 ^ 2 + 3 ^ 2 + 4 ^ 2 +. + 123456789 ^ 2

The last digit of 1 ^ 2 + 2 ^ 2 + 3 ^ 2 + 4 ^ 2 +. + 123456789 ^ 2 is 1 ^ 2 + 2 ^ 2 +... + 10 ^ 21 + 4 + 9 + 16 + 25 + 36 + 49 + 64 + 81 + 100, the last digit is 1 ^ 2 + 2 ^ 2 +... + 10 ^ 2 = 5, the last digit is 1 ^ 2 + 2 ^ 2 +... + 10 ^ 2 = the last digit is 11 ^ 2 + 12 ^ 2 +... + 20 ^ 2 = the last digit is 21 ^ 2 + 22 ^ 2 +... + 30 ^ 2 =... = 51 ^ 2 + 2 ^ 2 + 3 ^ 2 + 4 ^ 2 +

Find 1 * 1,2 * 2,3 * 3 123456789*123456789
The sum of the number of single digits

Step 1: construct recursive sequence formula (K + 1) & sup3; - K & sup3; = 3K & sup2; + 3K + 1 ① step 2: make recursive (column vertical addition) k = 1 into ① 2 & sup3; - 1 & sup3; = 3 * 1 & sup2; + 3 * 1 + 1K = 2 into ① 3 & sup3; - 2 & sup3; = 3 * 2 & sup2; + 3 * 2 + 1 K = n into (n + 1) & sup3; - N & S

Use 123456789 to form three three digit numbers, and the result is equal to 1998

985+672+341=1998
In fact, there are many solutions. You can switch positions between the hundreds of the three three digit numbers, between the tens and the tens, and between the bits. In fact, you need to add up three hundreds to 18, three tens to 19, and three digits to 8