[rPantoja]

Mathematically, there cannot be brackets or braces in a problem that does not have parentheses. Likewise, there cannot be braces in a problem that does not have both parentheses and brackets.

I found this website when I search the sentences above in GOOGLE.
I did so because I found those sentences in some instructional materials. I could also find the exact same quote in several educational websites. School districts and State Departments of Education equally repeat these guidelines, but they are simply incorrect.
While there is a widely accepted hierarchy for grouping symbols, nothing in MATHEMATICS forbids the use of brackets of braces in the absence of parenthesis. The expressions below may not be the most elegant, but they are perfectly “legal” mathematically speaking:

[x+1]
(3[2^4+1] +17)^2
[2x+3]*[x+1]
2x + [x+1]^2 + (y-2)
([2x+3]*[x+1])^2
(2^3 + [3^2 + √(2) ])

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