Observe the following list of regular numbers: 1 / 2, 1 / 6, 1 / 12, 1 / 30, 1 / 42 (2) 1 / 272 is the number one in the column_ individual (3) Calculate the sum of the first 20 numbers

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• 1. Observe the following regular numbers: 1 / 2, 1 / 6, 1 / 12, 1 / 20, 1 / 30, 1 / 42... Write the seventh and N numbers according to the law
• 2. Observe the following regular numbers: 1 / 2, 1 / 6, 1 / 12, 1 / 20, 1 / 30, 1 / 42... What is the seventh? 1 / 380? What is the nth?
• 3. A column of numbers 0, negative 2,6, negative 12,20, negative 30,42, etc. write the eighth number and the nth number according to this rule Ask for answers
• 4. 1.2.4.7. ().16.22 write the number according to the rule
• 5. Observe this series of regular numbers: 1 / 2, 1 / 6, 1 / 12, 1 / 30, 1 / 42, and know what the nth number is according to the law
• 6. Observe the following equations, find the laws from them, and use them to find the values of the following equations Look at the following equations: 1/√2+1=√2-1,1/√3-√2,1/√4-√3,1/√5+√4=√5-√4,… Find the laws from the above equations and use them to find the values of the following equations 1/√2+1+1/√3+√2+1/√4+√3+…… +1/√2013+√2012
• 7. 32-12=8×1；52-32=8×2；72-52=8×3… Observe the above formula, what law can you find? Please use algebra to express, and use this law to calculate the value of 20012-19992
• 8. Carefully observe the rules of the following group of formulas and write two such formulas: 99-27 = 72, 88-35 = 53, 77-25 = 52, 55-23 = 32
• 9. Observe the following three groups of formulas, find the rules and fill in the blanks 1 × 2 = 2 × 3 of 3, 1 × 2 + 2 × 3 = 2 × 3 × 4 of 3, 1 × 2 + 2 × 3 + 3 × 4 = 3 × 4 × 5 of 3 (1) 1 × 2 + 2 × 3 + 3 × 4 + 4 × 5 = 4 × 5 × () (2) 1 × 2 + 2 × 3 + 3 × 4 + 4 × 5 + 5 × 6 = () × () × () （3）1×2+2×3+3×4+… +N × (n + 1) = () × () × () (4) 1 × (1 × 2 + 2 × 3 + 3 × 4 +) + 199 × 200) = (this one needs to be written)
• 10. Observe each of the following formulas and fill in the blanks according to the rules you find 4*5=20,3*6=18 5*6=30,4*7=28 6*7=42,5*8=40 . If 1222 * 1223 = 1494506, then 1221 * 1224 = () Write the relationship
• 11. 1/2,1/6,1/12,1/30,1/42…… Find the rule, the nth number is () 1 / 132 is the number
• 12. 1 / 2, 1 / 6, 1 / 12, 1 / 20, 1 / 30, 1 / 42. According to the law, the seventh number is. The nth number is. 1 / 132 is the number
• 13. Formula calculation: 42 is 1 / 6 more than bracket
• 14. The law calculation of 1 / 12 + 1 / 20 + 1 / 30 + 1 / 42 + 1 / 56
• 15. Simple calculation 90.909-9.09 + 90.9
• 16. Ask a math question, the question is like this. 90.2 △ 75.1, find the quotient to you and check! Find the formula! I think it's our usual algorithm, which is used to eliminate the decimal point of the number! It's 75.1 △ 90.2
• 17. We need the formula! There is a batch of rice in the canteen. After eating one third of the rice, they bought 35 bags. The rice in the canteen is one fourth more than before. How many bags of rice are there in the canteen?
• 18. If the height of a cylindrical bucket is changed to twice the original height and the bottom diameter is changed to half the original diameter, it can hold 40 kg of water, then the original bucket can hold water______ Kilogram
• 19. 5 / 7 + 1 / 4-5 / 7
• 20. It is easy to calculate if you can 1.37.3-1.5/0.24=? 2.0.8x（20-1.25）=? 3.78/0.25/0.4=? Special reminder is out of formula calculation!