8z-5(6+z)-4*z*z-20=

Solution for 8z-5(6+z)-4*z*z-20= equation:

Simplifying
8z + -5(6 + z) + -4z * z + -20 = 0
8z + (6 * -5 + z * -5) + -4z * z + -20 = 0
8z + (-30 + -5z) + -4z * z + -20 = 0

Multiply z * z
8z + -30 + -5z + -4z2 + -20 = 0

Reorder the terms:
-30 + -20 + 8z + -5z + -4z2 = 0

Combine like terms: -30 + -20 = -50
-50 + 8z + -5z + -4z2 = 0

Combine like terms: 8z + -5z = 3z
-50 + 3z + -4z2 = 0

Solving
-50 + 3z + -4z2 = 0

Solving for variable 'z'.

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

Divide each side by '-4'.
12.5 + -0.75z + z2 = 0

Move the constant term to the right:

Add '-12.5' to each side of the equation.
12.5 + -0.75z + -12.5 + z2 = 0 + -12.5

Reorder the terms:
12.5 + -12.5 + -0.75z + z2 = 0 + -12.5

Combine like terms: 12.5 + -12.5 = 0.0
0.0 + -0.75z + z2 = 0 + -12.5
-0.75z + z2 = 0 + -12.5

Combine like terms: 0 + -12.5 = -12.5
-0.75z + z2 = -12.5

The z term is -0.75z.  Take half its coefficient (-0.375).
Square it (0.140625) and add it to both sides.

Add '0.140625' to each side of the equation.
-0.75z + 0.140625 + z2 = -12.5 + 0.140625

Reorder the terms:
0.140625 + -0.75z + z2 = -12.5 + 0.140625

Combine like terms: -12.5 + 0.140625 = -12.359375
0.140625 + -0.75z + z2 = -12.359375

Factor a perfect square on the left side:
(z + -0.375)(z + -0.375) = -12.359375

Can't calculate square root of the right side.

The solution to this equation could not be determined.