4r^2+9r-8=0

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Solution for 4r^2+9r-8=0 equation:


Simplifying
4r2 + 9r + -8 = 0

Reorder the terms:
-8 + 9r + 4r2 = 0

Solving
-8 + 9r + 4r2 = 0

Solving for variable 'r'.

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

Divide each side by '4'.
-2 + 2.25r + r2 = 0

Move the constant term to the right:

Add '2' to each side of the equation.
-2 + 2.25r + 2 + r2 = 0 + 2

Reorder the terms:
-2 + 2 + 2.25r + r2 = 0 + 2

Combine like terms: -2 + 2 = 0
0 + 2.25r + r2 = 0 + 2
2.25r + r2 = 0 + 2

Combine like terms: 0 + 2 = 2
2.25r + r2 = 2

The r term is 2.25r.  Take half its coefficient (1.125).
Square it (1.265625) and add it to both sides.

Add '1.265625' to each side of the equation.
2.25r + 1.265625 + r2 = 2 + 1.265625

Reorder the terms:
1.265625 + 2.25r + r2 = 2 + 1.265625

Combine like terms: 2 + 1.265625 = 3.265625
1.265625 + 2.25r + r2 = 3.265625

Factor a perfect square on the left side:
(r + 1.125)(r + 1.125) = 3.265625

Calculate the square root of the right side: 1.807104037

Break this problem into two subproblems by setting 
(r + 1.125) equal to 1.807104037 and -1.807104037.

Subproblem 1

r + 1.125 = 1.807104037 Simplifying r + 1.125 = 1.807104037 Reorder the terms: 1.125 + r = 1.807104037 Solving 1.125 + r = 1.807104037 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-1.125' to each side of the equation. 1.125 + -1.125 + r = 1.807104037 + -1.125 Combine like terms: 1.125 + -1.125 = 0.000 0.000 + r = 1.807104037 + -1.125 r = 1.807104037 + -1.125 Combine like terms: 1.807104037 + -1.125 = 0.682104037 r = 0.682104037 Simplifying r = 0.682104037

Subproblem 2

r + 1.125 = -1.807104037 Simplifying r + 1.125 = -1.807104037 Reorder the terms: 1.125 + r = -1.807104037 Solving 1.125 + r = -1.807104037 Solving for variable 'r'. Move all terms containing r to the left, all other terms to the right. Add '-1.125' to each side of the equation. 1.125 + -1.125 + r = -1.807104037 + -1.125 Combine like terms: 1.125 + -1.125 = 0.000 0.000 + r = -1.807104037 + -1.125 r = -1.807104037 + -1.125 Combine like terms: -1.807104037 + -1.125 = -2.932104037 r = -2.932104037 Simplifying r = -2.932104037

Solution

The solution to the problem is based on the solutions from the subproblems. r = {0.682104037, -2.932104037}

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