t^2=21-4t

Solution for t^2=21-4t equation:

Simplifying
t2 = 21 + -4t

Solving
t2 = 21 + -4t

Solving for variable 't'.

Reorder the terms:
-21 + 4t + t2 = 21 + -4t + -21 + 4t

Reorder the terms:
-21 + 4t + t2 = 21 + -21 + -4t + 4t

Combine like terms: 21 + -21 = 0
-21 + 4t + t2 = 0 + -4t + 4t
-21 + 4t + t2 = -4t + 4t

Combine like terms: -4t + 4t = 0
-21 + 4t + t2 = 0

Factor a trinomial.
(-7 + -1t)(3 + -1t) = 0

Subproblem 1
Set the factor '(-7 + -1t)' equal to zero and attempt to solve:

Simplifying
-7 + -1t = 0

Solving
-7 + -1t = 0

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

Add '7' to each side of the equation.
-7 + 7 + -1t = 0 + 7

Combine like terms: -7 + 7 = 0
0 + -1t = 0 + 7
-1t = 0 + 7

Combine like terms: 0 + 7 = 7
-1t = 7

Divide each side by '-1'.
t = -7

Simplifying
t = -7
Subproblem 2
Set the factor '(3 + -1t)' equal to zero and attempt to solve:

Simplifying
3 + -1t = 0

Solving
3 + -1t = 0

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

Add '-3' to each side of the equation.
3 + -3 + -1t = 0 + -3

Combine like terms: 3 + -3 = 0
0 + -1t = 0 + -3
-1t = 0 + -3

Combine like terms: 0 + -3 = -3
-1t = -3

Divide each side by '-1'.
t = 3

Simplifying
t = 3
Solution
t = {-7, 3}