in general ive been having trouble factoring polynomials because the steps dont seem to mean anything, and it seems more like simplifying than factoring even though i guess those are similar?
but onto more pressing matters. my book factors trinomials with substitution as such:
consider trinomial 3x^2 - 2x - 8
step 1: multiply ax^2 + bx + c by a to transform x^2 into (ax)^2.
i dont understand why we do this, no other video has done this before. i'd understand this step if the 3x^2 term was to equal 3(3x^2) which i think would be 9x^2 but it doesn't equal that. in general, i dont know what "transform x^2 into (ax)^2" really means. or why we do this when other videos have a common binomial substitution which i can do easily. after the supposed multiplication of 3 to every term, we have:
(3x)^2 - 2(3x) - 24
(Why isn't 2(3x) just 6x???????? why is - 24 not -24x since in some places we multiply by 3x and others by 3??)
replace ax with a variable p. p = ax.
we now have p^2 - 2p - 24. the typical factoring commences where c = pq and b = p + q.
we now have (p - 6)(p + 4). we substitute ax back into p.
(3x - 6)(3x + 4)
3(x - 2)(3x + 4) factoring out common factors we end up with (x - 2)(3x + 4) im under the impression the common factor of the second binomial was 1 which i've never seen before. but that doesn't make sense as what did we divide 2 by then?
and then since we started by multiplying the trinomial by a , we must divide by a, and this obviously doesn't make sense to me as someone not behind the reason we multiplied by a. the answer is (x - 2)(3x + 4)
we have the easier and obvious method of AC grouping (i dont get it but its consistent so whatever) but we also have substitution and im scared i might get a question asking me to factor by substitution specifically in our upcoming midterm.
help to understand or other resources much appreciated.