What is the purpose of brackets in a quotation?

Hey, I found this

”When writers alter words in a direct quotation, square brackets—[ ]—are placed around the change. The brackets, always used in pairs, enclose words intended to clarify meaning, provide a brief explanation, or to help integrate the quote into the writer's sentence.”

When writers alter words in a direct quotation, square brackets—[ ]—are placed around the change. The brackets, always used in pairs, enclose words intended to clarify meaning, provide a brief explanation, or to help integrate the quote into the writer's sentence.

Explanation:

(I took it from the guy above, but you can just copy mine easier)

Have a good day :)

"Use Pythagorean Theorem to solve (a right triangle with the base being one of the side lengths and the height being the other side length.  a^2 + b^2 = c^2
64^2 + 100^2 = length of diagonal ^2
4096 + 10000 = 14096
The length of the diagonal is the square root of 14096 or 118.727 meters (rounded to the thousandths place). "
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hope this helps!!