Number 7. Please asap.

7a)

If n is the amount of sides then there's 38 sides in a polygon with 665 diagonals

7b)

We do the same as 7a) but with 406. We get that and . A polygon cant have 30.04 sides

A. 38 sides

B. When solved, you get -27.04 sides or 30.04 sides. Neither of these are possible because the number of sides cannot be negative or a decimal.

Step-by-step explanation: Part A:

If the polygon has 665 diagonals, set your original n-sided polygon equal to it.

n(n - 3)/2 = 665

Multiply both sides by 2 so it’s not in the denominator.

n(n - 3) = 1330

Distribute n and subtract 1330 from both sides so it is equal to zero.

n² - 3n - 1330 = 0

Factor it:

(n - 38)(n * 35) = 0

Solve for n by setting it equal to zero:

n = 38 & n = -35

The number of sides cannot be negative, therefore, the answer to Part A is 38 sides.

Part B:

Set your original n-sided polygon equal to 406 and solve to prove that a polygon cannot have 406 diagonals.

n(n - 3)/2 = 406

Multiply both sides by 2 so it’s not in the denominator.

n(n - 3) = 812

Distribute n and subtract 812 from both sides so that it is equal to zero.

n² - 3n - 812 = 0

This cannot be factored, so plug it into the Quadratic Formula. Here are the values you need for the Quadratic Formula based on the polynomial above:

a = 1

b = -3

c = -812

When you solve this, you will get:

n = -27.04 and n = 30.04

A polygon cannot have negative sides and it cannot have decimal sides. It has to be a positive integer (positive whole number).

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.