Please check these answers.

Multiply
-7(2a2 -4) = -14a2 + 28

Multiply
0.5(a + b -5) = 0.5a + 0.5b - 2.5

Factor
bx - by + bz = b(x - y + z)

Combine like terms (simplify)
12x + 4 - 11y - 6x - 9 - y = 6x - 12y - 5

Evaluate the expression
3x2y when x = 3 and y = 5
Answer: 135

Write as a fraction and simplify
Z-4
Answer: 1/z-4

Write using negative exponents
1/64
Answer: -6-4

Multiply and simplify
3-small2 • 3small6 = 81

Divide and simplify
4-small2/4small4 = 16

Divide and simplify
Y/y-5 = 1

Simplify
(2small3) -small2 =32

Simplify
(x-small1 ysmall1) small5 = ysmall5/xsmall5

Write in scientific notation
0.000005 = 5x10 -small6

Write in standard notation
31 x 10small7 =310,000,000

Perform the indicated operations (give your answer in scientific notation)
(5x10small2) x (5.6x10small4) = 2.8x10small6

Solve
X - 2.1 = -7.5
Answer: x = -5.4

Solve
2.3 = -y/2
Answer: y = -4.6

Solve
2 - x = 11 (x - 1)
Answer: x = 13/12

Please check my answers.

check # 7 and 9

Simplify the expression 2√20-3√7-2√5+4√63 please help the is A because nothing change

Let's go through each question and check your answers.

1. Multiply: -7(2a^2 -4) = -14a^2 + 28
Your answer is correct.

2. Multiply: 0.5(a + b -5) = 0.5a + 0.5b - 2.5
Your answer is correct.

3. Factor: bx - by + bz = b(x - y + z)
Your answer is correct.

4. Combine like terms (simplify): 12x + 4 - 11y - 6x - 9 - y = 6x - 12y - 5
Your answer is correct.

5. Evaluate the expression: 3x^2y when x = 3 and y = 5
Your answer is correct.

6. Write as a fraction and simplify: Z-4
I believe there might be a mistake in your answer. The correct answer should be 1/(Z-4).

7. Write using negative exponents: 1/64
Your answer is correct.

8. Multiply and simplify: 3^2 • 3^6 = 3^8 = 6561
Your answer is incorrect. The correct answer is 3^8 = 6561.

9. Divide and simplify: 4^2 / 4^4
Your answer is incorrect. The correct answer is 4^2 / 4^4 = 1/4^2 = 1/16.

10. Divide and simplify: Y/(y-5) = 1
Your answer is correct.

11. Simplify: (2^3) ^ -2
Your answer is correct.

12. Simplify: (x^(-1) y) ^ 5
Your answer is correct.

13. Write in scientific notation: 0.000005 = 5x10^-6
Your answer is correct.

14. Write in standard notation: 31 x 10^7 = 310,000,000
Your answer is correct.

15. Perform the indicated operations (give your answer in scientific notation): (5x10^2) x (5.6x10^4) = 2.8x10^7
Your answer is correct.

16. Solve: X - 2.1 = -7.5
Your answer is correct.

17. Solve: 2.3 = -y/2
Your answer is correct.

18. Solve: 2 - x = 11 (x - 1)
Your answer is correct.

Overall, you did a great job on these questions! Your answers are correct for most of them, with a few mistakes. Be sure to double-check your calculations and be careful with negative exponents and fractions. Great work!