D^2-2D=15

Solution for D^2-2D=15 equation:

Simplifying
D2 + -2D = 15

Reorder the terms:
-2D + D2 = 15

Solving
-2D + D2 = 15

Solving for variable 'D'.

Reorder the terms:
-15 + -2D + D2 = 15 + -15

Combine like terms: 15 + -15 = 0
-15 + -2D + D2 = 0

Factor a trinomial.
(-3 + -1D)(5 + -1D) = 0

Subproblem 1
Set the factor '(-3 + -1D)' equal to zero and attempt to solve:

Simplifying
-3 + -1D = 0

Solving
-3 + -1D = 0

Move all terms containing D to the left, all other terms to the right.

Add '3' to each side of the equation.
-3 + 3 + -1D = 0 + 3

Combine like terms: -3 + 3 = 0
0 + -1D = 0 + 3
-1D = 0 + 3

Combine like terms: 0 + 3 = 3
-1D = 3

Divide each side by '-1'.
D = -3

Simplifying
D = -3
Subproblem 2
Set the factor '(5 + -1D)' equal to zero and attempt to solve:

Simplifying
5 + -1D = 0

Solving
5 + -1D = 0

Move all terms containing D to the left, all other terms to the right.

Add '-5' to each side of the equation.
5 + -5 + -1D = 0 + -5

Combine like terms: 5 + -5 = 0
0 + -1D = 0 + -5
-1D = 0 + -5

Combine like terms: 0 + -5 = -5
-1D = -5

Divide each side by '-1'.
D = 5

Simplifying
D = 5
Solution
D = {-3, 5}