:simplify: 1. 3x^2+4x+3x^2-4y 2. (5x-+8y) 3. 3x^3(2x)^2 4. (-6a^3b^4)^2 5. (x+9) (x-9) 6. (3x-7)^2 7. (3x+6) (4x-7)

1. 6x^2 + 4x - 4y

2. x - 10y.

3. 6x^5

4.  36 a^6 b^8

5. x^2 - 81

6. 9x^2 - 42x + 49

7. 12x^2 +3x - 42

Step-by-step explanation:

1. 3x^2+4x+3x^2-4y

Add the like terms, we get

6x^2 + 4x - 4y

2. (5x-2y)-(4x+8y)

Now distribute the negative sign, we get

5x - 2y -4x -8y

Simplify the like terms, we get

x - 10y.

3. 3x^3(2x)^2

Multiply the numbers and simplify the variables

6x^(3 +2)

6x^5

4. (-6a^3b^4)^2

Now bring the power 2 inside the parenthesis.

-6^2 a^6 b^8

= 36a^6b^8

5. (x+9) (x-9)

x^2 + 9x -9x - 81

x^2 - 81

6. (3x-7)^2

(3x - 7)(3x - 7)

9x^2 - 21x -21x + 49

9x^2 - 42x + 49

7. (3x+6) (4x-7)

12x^2 + 24x -21x - 42

12x^2 +3x - 42

Thank you.