1.4y^2+5.6y-16.8=0

Solution for 1.4y^2+5.6y-16.8=0 equation:

Simplifying
1.4y2 + 5.6y + -16.8 = 0

Reorder the terms:
-16.8 + 5.6y + 1.4y2 = 0

Solving
-16.8 + 5.6y + 1.4y2 = 0

Solving for variable 'y'.

Begin completing the square.  Divide all terms by
1.4 the coefficient of the squared term: 

Divide each side by '1.4'.
-12 + 4y + y2 = 0

Move the constant term to the right:

Add '12' to each side of the equation.
-12 + 4y + 12 + y2 = 0 + 12

Reorder the terms:
-12 + 12 + 4y + y2 = 0 + 12

Combine like terms: -12 + 12 = 0
0 + 4y + y2 = 0 + 12
4y + y2 = 0 + 12

Combine like terms: 0 + 12 = 12
4y + y2 = 12

The y term is 4y.  Take half its coefficient (2).
Square it (4) and add it to both sides.

Add '4' to each side of the equation.
4y + 4 + y2 = 12 + 4

Reorder the terms:
4 + 4y + y2 = 12 + 4

Combine like terms: 12 + 4 = 16
4 + 4y + y2 = 16

Factor a perfect square on the left side:
(y + 2)(y + 2) = 16

Calculate the square root of the right side: 4

Break this problem into two subproblems by setting 
(y + 2) equal to 4 and -4.

Subproblem 1
y + 2 = 4

Simplifying
y + 2 = 4

Reorder the terms:
2 + y = 4

Solving
2 + y = 4

Solving for variable 'y'.

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

Add '-2' to each side of the equation.
2 + -2 + y = 4 + -2

Combine like terms: 2 + -2 = 0
0 + y = 4 + -2
y = 4 + -2

Combine like terms: 4 + -2 = 2
y = 2

Simplifying
y = 2

Subproblem 2
y + 2 = -4

Simplifying
y + 2 = -4

Reorder the terms:
2 + y = -4

Solving
2 + y = -4

Solving for variable 'y'.

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

Add '-2' to each side of the equation.
2 + -2 + y = -4 + -2

Combine like terms: 2 + -2 = 0
0 + y = -4 + -2
y = -4 + -2

Combine like terms: -4 + -2 = -6
y = -6

Simplifying
y = -6

Solution
The solution to the problem is based on the solutions
from the subproblems.
y = {2, -6}