How can you factor a quadratic expression like 2x^2 + 7x + 3 using the AC method or factoring by grouping? What’s the key difference between these two approaches?

Answer 1

2x^2 +7x +3 = (2x+1)(x+3)

if you can't see the factors, which are fairly obvious, by default you can always use the quadratic formula and solve for the roots, then change the sign of the roots and stick and x in front of them. Multiply them together

x = -7/4 + or - (1/4)sqr(49 -24) = -7/4 +/-5/4 = -12/4 or -2/4 = 3 or -1/2

(x+1/2)(x+3) but you need a 2 as coefficient of the x^2 term so

go with (2x+1)(x+3)

integer factors would have integer factors of the constant term over integer factors of the x^2 term's coefficient, so that narrows it down to +/- 3/2, 3/1, 1/2 or 1/1 = +/- 3/2,3, 1/2 or 1

x+/-3/2, x+/-3, x+/-1/2, and x+/-1

Answer 2

When the leading coefficient (A) is 1, you can use the AC method only to factor. When the leading coefficient is anything besides 1, you use both the AC method followed by factoring by grouping.

I hope this video helps.

Answer 3

I always have my students use the AC method with grouping for any quadratic with a leading coefficient that isn't a 1. The reason that I like it is that it gives them an algorithm that is completely mathematically based. I have a full explanation of the process with several examples here: https://drive.google.com/drive/u/0/folders/1kW9g_mbtUjCzDwh6ga-zaqB5OxCQVMyu

Answer 4

To factor 2x² + 7x + 3 using the AC method, multiply AC to get (2)(3)=6 and rewrite the trinomial as

x² + 7x + 6.

Now find products of 6 that add to 7, which are 1 and 6 (since (1)(6)=6 and 1+6=7). Write the trinomial in factored form using 1 and 6 to get (x + 1)(x + 6). Next, divide each number by the original leading coefficient 2 to get (x + 1/2)(x + 6/2). If you can reduce any of the fractions do so: (x + 1/2)(x + 3). For fractions that are not reduceable bring the denominator in front of the x to get (2x + 1)(x + 3). Finished!

To factor 2x² + 7x + 3 using the grouping method, start out as we did in the first example by multiplying AC to get (2)(3)=6, and finding products of 6 that add to 7, which are 1 and 6 (since (1)(6)=6 and 1+6=7). Now put an x after each of your numbers to get 1x and 6x. We will substitute those in for the 7x to get:

2x² + 6x + 1x + 3. Now we can group the terms into two groups as follows: 2x² + 6x and +1x + 3 (notice I kept the + sign in front of the 1 since it was positive in the expression. That will be part of the GCF as you will see.) Now factor out the GCF for each of the groups to get: 2x(x + 3) and +1(x + 3). Since both parenthesis match, that means the math was done correctly. For the final answer, combine the two GCFs to get (2x + 1) and keep one of the parenthesis (x + 3). The final answer is (2x + 1)(x + 3). Finished!