Squares and absolute values are non-negative numbers.
Both squares and absolute values are non-negative numbers.
Squares, and also absolute values, are non-negative number
Squares are non-negative numbers, as also are absolute values.
Squares, as well as absolute values, are non-negative numbers.
not only ... but also (强调有多于一个可能性)
Not only squares but also absolute values are non-negative numbers.
apart from/in addition to (强调多于一种方法;比用also稍微更强调平方，但比用not only ... but also强调弱些)
Apart from (In addition to) squares, absolute values are non-negative numbers.
moreover/furthermore (着重在moreover/furthermore后面的叙述)
Squares and absolute values are two of the commonest non-negative numbers. Moreover (Furthermore), principal square roots are well known.
