Indirect Proofs: Shaping the Proof

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Indirect proofs are a mathematical technique where one assumes the negation of the statement to be proved and works towards a contradiction. This method, known as "proof by contradiction," involves three key steps: assuming the opposite of the desired conclusion, applying logical reasoning to derive a contradiction, and concluding that the original assumption is false. By reaching a contradiction, the original statement is indirectly validated as true. Although it may seem counterintuitive initially, mastering indirect proofs can enhance problem-solving skills in mathematics. Practicing this approach can make it a valuable addition to one's mathematical toolkit.
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Hey, anyone ever done indirect proofs? Maybe my school is a little weird, but we are doing those. IF you did, how do we shape the proof?
 
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You have to assume the statement to be proved is false and then work towards a contradiction.
 

Indirect proofs are a common and useful method in mathematics. They involve proving a statement by assuming its negation and then reaching a contradiction. This allows us to indirectly prove the original statement is true.

To shape an indirect proof, we typically follow three steps:

1. Assume the opposite: We begin by assuming the opposite of what we want to prove. This is called the "proof by contradiction" approach.

2. Use logical reasoning: Next, we use logical reasoning to reach a contradiction. This can involve using previously proven theorems or definitions, as well as using the properties of numbers or geometric figures.

3. Reach a contradiction: Finally, we reach a contradiction, which proves that our original assumption must be false. This, in turn, proves that our original statement is true.

In summary, shaping an indirect proof involves starting with an assumption, using logical reasoning to reach a contradiction, and ultimately proving the original statement by contradiction. It may seem counterintuitive at first, but with practice, indirect proofs can be a powerful tool in your mathematical toolkit. Good luck with your proofs!
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
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