Strictly speaking, 'a creative activity' is indeed a noun.

According to Garner (Garner's Modern American Usage is considered one of the authoritative references), like is adjectival and as is adverbial.

If you think of 'a creative activity' as an action rather than as a noun, you can see why this SC question is debatable.

For example, you would approach something *cautiously*. (adverb)
If you were to approach something *cautious* (adjective), cautious would describe the something, not the manner in which you approach it.

Since we intend to describe the manner in which to approach mathematics, the adverbial *as* seems appropriate.

English is full of exceptions, and exceptions to those exceptions. I didn't even know most of them, or for that matter even what a gerund is, until I started teaching, and I scored a 770. Keep your head up, and do your best to learn the majority of the rules. However, focus on your test-taking process rather than worrying about learning 20,000 facts. The process is far more important!

could also be

to approach mathematics as (if it were) a creative activity or to force students to memorize rules and principles

that is how i read it

this way less confusion no?

Like to similar nouns
as is used for clauses, here they are talking about two diff ways to teach maths so as is correct.