Answer:
b=31 in
![ax^2+bx+c](https://img.qammunity.org/2022/formulas/mathematics/college/ls8sd3d86nio6ip6c65icmceeplhmx8zo2.png)
Explanation:
Hi there!
![( 4x - 2 ) ( x + 9 ) - 3x](https://img.qammunity.org/2022/formulas/mathematics/high-school/fgbljl6d2jpp2xo379zx94einah9x7kfwd.png)
Our goal is to expand this equation and put it in the form
. Firstly, multiply the first two binomials (in the parentheses):
![= 4x(x+9)-2(x+9)-3x\\= 4x^2+36x-2(x+9)-3x\\= 4x^2+36x-2x-18-3x](https://img.qammunity.org/2022/formulas/mathematics/high-school/iprpp08kkbweldkuwnepzeaq5e7lbq9lnh.png)
Now, we can combine like terms (terms with like variables):
![= 4x^2+36x-2x-3x-18\\= 4x^2+31x-18](https://img.qammunity.org/2022/formulas/mathematics/high-school/gyq5w4okbp0g0h3twlx7ule55x7nlp5j1z.png)
Now, in this equation, we can easily identify that 31 is the value of b in
.
I hope this helps!