64+16x^2-72x+81=289 I don’t understand

x = 6 or x = -3/2

Step-by-step explanation:

Solve for x:

16 x^2 - 72 x + 145 = 289

Hint: | Write the quadratic equation in standard form.

Divide both sides by 16:

x^2 - (9 x)/2 + 145/16 = 289/16

Hint: | Solve the quadratic equation by completing the square.

Subtract 145/16 from both sides:

x^2 - (9 x)/2 = 9

Hint: | Take one half of the coefficient of x and square it, then add it to both sides.

Add 81/16 to both sides:

x^2 - (9 x)/2 + 81/16 = 225/16

Hint: | Factor the left hand side.

Write the left hand side as a square:

(x - 9/4)^2 = 225/16

Hint: | Eliminate the exponent on the left hand side.

Take the square root of both sides:

x - 9/4 = 15/4 or x - 9/4 = -15/4

Hint: | Look at the first equation: Solve for x.

Add 9/4 to both sides:

x = 6 or x - 9/4 = -15/4

Hint: | Look at the second equation: Solve for x.

Add 9/4 to both sides:

 x = 6 or x = -3/2

14.3

step-by-step explanation:

add all the numbers together.

9 + 12 + 15 + 16 + 17 + 17 = 86

now, divide 86 by how many numbers we have: 6.

86 / 6 = 14.3