# Q10, the one on the top matters! | Summary and Q&A

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August 18, 2018
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Q10, the one on the top matters!

## TL;DR

Learn how to solve integrals using the substitution method by making appropriate substitutions and simplifying the expressions.

## Key Insights

• ð The substitution method is a powerful technique for solving integrals by making appropriate substitutions.
• ð The choice of the substitution variable depends on the expression within the integral and its derivative.
• ð Integrals can be simplified by canceling terms and bringing them into a more manageable form.
• ðĪŠ Going back to the original variable world is essential to match the original integral's form.
• â Different substitutions can be used for different integrals, showcasing the flexibility of the method.
• â The substitution method can solve complex integrals that may appear daunting at first.
• ð It is important to carefully choose substitutions to simplify the expression as much as possible.

## Transcript

okay we are going to do this one first because we can just use a new sub let u equal to the inside I will just put down u equal two times cosine X minus one and we know this is a good choice because if I differentiate both sides the derivative of two cos x minus one is negative 2 sine X DX and I want to isolate this DX I can justify this on both si... Read More

### Q: How is the substitution method useful in solving integrals?

The substitution method helps simplify integrals by substituting a variable, making the process of integration more manageable. It simplifies complicated expressions and allows for easier integration.

### Q: Why is u = 2cos(x) - 1 chosen as the substitution variable?

u = 2cos(x) - 1 is chosen because its derivative, -2sin(x), is present in the integral. This choice cancels out the sine terms, making it easier to integrate.

### Q: What happens if a different substitution is chosen for the second integral?

If a different substitution, u = â(2cos(x) - 1), is chosen, the result is still solvable. It demonstrates that different substitutions can be used to simplify and solve integrals.

### Q: Why is it necessary to go back to the x world after solving in the u world?

Going back to the x world is necessary because the integral was initially defined in terms of x. The final answer needs to be in terms of x to match the original integral.

## Summary & Key Takeaways

• The video explains how to solve integrals using the substitution method.

• A step-by-step process is demonstrated for solving the first integral with the substitution u = 2cos(x) - 1.

• The second integral is solved using a different substitution, letting u = â(2cos(x) - 1).

• Both integrals are simplified and solved, resulting in the final answers.