7n^2-4n-14=21
complete the square

(7n - 2)² = 249

Explanation:

1) Given expression: 7n² - 4n - 14 = 21

2) Transpose  - 14 =>

7n² - 4n = 21 + 14

3) Combine like terms =>

7n² - 4n = 35

4) multiply both terms by 7 =>

(7n)² - 4(7n) = 35×7

5) form the squared binomial:

(7n - 2)² - 4 = 35×7

6) Transpose - 4 =>

(7n - 2)² = 35×7 + 4

7) Do the operations on the right side:

(7n - 2)² = 249 or (7n - 2)² - 249 = 0

8) Verify the equivalence by expanding the binomial:

(7n)² - 2(7n) + 4 - 249 = 0

(7n)² - 14n - 245 = 0

Divide by 7: 7n² - 2n - 35 = 0 or 7n² - 2n = 35, which is equivalent to the given expression.

(6,0) i hope it makes enough sense