(21)x*x-6=15x

Solution for (21)x*x-6=15x equation:

Simplifying
(21) * x * x + -6 = 15x

Multiply x * x
21x2 + -6 = 15x

Reorder the terms:
-6 + 21x2 = 15x

Solving
-6 + 21x2 = 15x

Solving for variable 'x'.

Reorder the terms:
-6 + -15x + 21x2 = 15x + -15x

Combine like terms: 15x + -15x = 0
-6 + -15x + 21x2 = 0

Factor out the Greatest Common Factor (GCF), '3'.
3(-2 + -5x + 7x2) = 0

Factor a trinomial.
3((-2 + -7x)(1 + -1x)) = 0

Ignore the factor 3.
Subproblem 1
Set the factor '(-2 + -7x)' equal to zero and attempt to solve:

Simplifying
-2 + -7x = 0

Solving
-2 + -7x = 0

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

Add '2' to each side of the equation.
-2 + 2 + -7x = 0 + 2

Combine like terms: -2 + 2 = 0
0 + -7x = 0 + 2
-7x = 0 + 2

Combine like terms: 0 + 2 = 2
-7x = 2

Divide each side by '-7'.
x = -0.2857142857

Simplifying
x = -0.2857142857
Subproblem 2
Set the factor '(1 + -1x)' equal to zero and attempt to solve:

Simplifying
1 + -1x = 0

Solving
1 + -1x = 0

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

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

Combine like terms: 1 + -1 = 0
0 + -1x = 0 + -1
-1x = 0 + -1

Combine like terms: 0 + -1 = -1
-1x = -1

Divide each side by '-1'.
x = 1

Simplifying
x = 1
Solution
x = {-0.2857142857, 1}