Here's is another question and solution from the same set as my previous question. This looks like another mistake in the solution to me. I have marked it with the green arrow. This is a typo right? Surely there should be no minus sign here?


Here's is another question and solution from the same set as my previous question. This looks like another mistake in the solution to me. I have marked it with the green arrow. This is a typo right? Surely there should be no minus sign here?


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:-)