Question

Find and correct errors of the following mathematical expressions:
$(y-3{)}^2=y^2-9$

Answer 1

The statement is incorrect.

It can be expanded by using formula $(a-b{)}^2$. But instead of this the formula used here is $a^2-b^2$ which is incorrect.
Therefore the correct statement is
$(y-3{)}^2=y^2-2\times y\times 3+9=y^2-6y+9$