Differential Equations Example confusion

Post date: 2019-07-18 05:04:40

I'm having a trouble following one step of an example in a differential equations textbook. It's an example demonstrating solving a Cauchy-Euler equation by using a substitution to convert it to an equation with constant coefficients.

I know its probably something pretty straightforward, but I'm not seeing it. Unfortunately I'm reviewing on my own right now, so I don't have someone else to ask. Can someone look at the step highlighted in green and explain to me what's going on there?

I figure I'll probably smack myself in the forehead when someone does, but at least I won't be hung up anymore.

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