4y^2+8y+-21=0

Solution for 4y^2+8y+-21=0 equation:

Simplifying
4y2 + 8y + -21 = 0

Reorder the terms:
-21 + 8y + 4y2 = 0

Solving
-21 + 8y + 4y2 = 0

Solving for variable 'y'.

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

Subproblem 1
Set the factor '(-7 + -2y)' equal to zero and attempt to solve:

Simplifying
-7 + -2y = 0

Solving
-7 + -2y = 0

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

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

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

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

Divide each side by '-2'.
y = -3.5

Simplifying
y = -3.5
Subproblem 2
Set the factor '(3 + -2y)' equal to zero and attempt to solve:

Simplifying
3 + -2y = 0

Solving
3 + -2y = 0

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

Add '-3' to each side of the equation.
3 + -3 + -2y = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -2y = 0 + -3
-2y = 0 + -3

Combine like terms: 0 + -3 = -3
-2y = -3

Divide each side by '-2'.
y = 1.5

Simplifying
y = 1.5
Solution
y = {-3.5, 1.5}