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manh
2 năm trước
1)Cho A=3+3^2+3^3+.....+3^100.Tìm n thuộc N biết 2A+3=3^4 2)So sánh : a)243^5 và 327^5 b)625^5 và 125^7 c)3^500 và 7^300 3)Tim số nguyên dương n biết: a)64<2^n<256 b)243>3^n>9 Giúp mik nhanh nhanh nha mai mik phải nộp rùi
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tóm tắt hộ mình bài này với Introduction When the sun comes out after it rains, run outside. You may see a rainbow in the sky. Rainbows are tricks made by light. We can see them, but we can't touch them or walk around them. They seem to move away when we try to get close to them. Science can explain how rainbows happen. Where and When Rainbows Appear Look around the next time you see a rainbow. The Sun will be shining from behind you. There will be rain in front of you, where you'll see the rainbow. We usually see a rainbow as a half-circle. It actually forms a full circle . From the ground , we can only see the top half. How Rainbows Form Years ago, a French scientist studied rainbows. He found that to see a rainbow , you must be in the right spot. Rainbows in Myths and Tales • Vikings said a rainbow bridge linked their gods to Earth. • In Ireland , people tell fairy tales about gold hidden at the ends of rainbows . Elves guard these pots of gold. •The Hindu god Indra is shown using a rainbow as an archer's bow to shoot lightning arrows. Knowing how light moves helps explain rainbows . Think of running on land. Now think of trying to run through water. You will move more slowly through water because it is thicker than air. In the same way , light moves faster through air than through water. As the light moves through water , it slows down and bends. Rainbows form when water drops meet sunlight. The light bends when it goes into each drop. Then it reflects, or bounces , off the back of each drop. The light bends again as it leaves the drop. This happens in millions of water drops at once , making the colors of a rainbow. The Colors of the Rainbow Sunlight is made up of many colors Water drops the sunlight into different colors. Splitting light makes a rainbow. You have to be in the right spot to see a rainbow. Each water drop reflects colored light at a slightly different angle. The colors of the rainbow always appear in the same order. The name ROY G. BIV can help you remember the seven main They are red , orange , yellow , green , blue , indigo, and violet. Make Your Own Rainbow 1. Fill a clear glass about three - quarters full of water. 2. Place the glass where sunlight can pass through it. 3. Hold a white piece of paper . Let the light shine through the water onto the paper . Move the paper around until you find a rainbow. 4. Use colored pencils to mark the different colors on the paper. How many can you see ? What order are they in? Conclusion Rain stops and the Sun comes out. A beautiful rainbow sweeps across the sky. Most people find it hard not to stop and stare when a rainbow appears. Science explains how rainbows form. Still , a rainbow is always a magical sight to see .

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