2a^2+5a-4=0

Solution for 2a^2+5a-4=0 equation:

Simplifying
2a2 + 5a + -4 = 0

Reorder the terms:
-4 + 5a + 2a2 = 0

Solving
-4 + 5a + 2a2 = 0

Solving for variable 'a'.

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

Divide each side by '2'.
-2 + 2.5a + a2 = 0

Move the constant term to the right:

Add '2' to each side of the equation.
-2 + 2.5a + 2 + a2 = 0 + 2

Reorder the terms:
-2 + 2 + 2.5a + a2 = 0 + 2

Combine like terms: -2 + 2 = 0
0 + 2.5a + a2 = 0 + 2
2.5a + a2 = 0 + 2

Combine like terms: 0 + 2 = 2
2.5a + a2 = 2

The a term is 2.5a.  Take half its coefficient (1.25).
Square it (1.5625) and add it to both sides.

Add '1.5625' to each side of the equation.
2.5a + 1.5625 + a2 = 2 + 1.5625

Reorder the terms:
1.5625 + 2.5a + a2 = 2 + 1.5625

Combine like terms: 2 + 1.5625 = 3.5625
1.5625 + 2.5a + a2 = 3.5625

Factor a perfect square on the left side:
(a + 1.25)(a + 1.25) = 3.5625

Calculate the square root of the right side: 1.887458609

Break this problem into two subproblems by setting 
(a + 1.25) equal to 1.887458609 and -1.887458609.

Subproblem 1
a + 1.25 = 1.887458609

Simplifying
a + 1.25 = 1.887458609

Reorder the terms:
1.25 + a = 1.887458609

Solving
1.25 + a = 1.887458609

Solving for variable 'a'.

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

Add '-1.25' to each side of the equation.
1.25 + -1.25 + a = 1.887458609 + -1.25

Combine like terms: 1.25 + -1.25 = 0.00
0.00 + a = 1.887458609 + -1.25
a = 1.887458609 + -1.25

Combine like terms: 1.887458609 + -1.25 = 0.637458609
a = 0.637458609

Simplifying
a = 0.637458609

Subproblem 2
a + 1.25 = -1.887458609

Simplifying
a + 1.25 = -1.887458609

Reorder the terms:
1.25 + a = -1.887458609

Solving
1.25 + a = -1.887458609

Solving for variable 'a'.

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

Add '-1.25' to each side of the equation.
1.25 + -1.25 + a = -1.887458609 + -1.25

Combine like terms: 1.25 + -1.25 = 0.00
0.00 + a = -1.887458609 + -1.25
a = -1.887458609 + -1.25

Combine like terms: -1.887458609 + -1.25 = -3.137458609
a = -3.137458609

Simplifying
a = -3.137458609

Solution
The solution to the problem is based on the solutions
from the subproblems.
a = {0.637458609, -3.137458609}