B. associative property
C. commutative property
Step-by-step explanation:
A complex number is defined by the form:
![a+bi \\ \\ Where: \\ \\ a,b \ are \ constant \ numbers \\ \\ i \ is \ the \ imaginary \ number](https://img.qammunity.org/2021/formulas/mathematics/middle-school/ql8sx84625qgyj25x7nog0w2fupd8sc3ic.png)
Here we use:
B. associative property
C. commutative property
Let's rewrite our expressions as:
Step 1.
![(5+2i)+(6+7i)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/2efiiyzb85h04rhaujd2tx72b17u7y877b.png)
Step 2.
![(5+6)+(2i+7i)](https://img.qammunity.org/2021/formulas/mathematics/middle-school/3dfp2s8mjz39mzlqvld6arn3zmjlgkn6p7.png)
Step 3.
![11+9i](https://img.qammunity.org/2021/formulas/mathematics/middle-school/toedyl52aqcgpqgyprychv3uqp4xjv24h0.png)
So in step 2 we apply those properties because we make the commutation of 6 and 2i and perform the association using parentheses.