a^2+4ab-21b^2=

Solution for a^2+4ab-21b^2= equation:

Simplifying
a2 + 4ab + -21b2 = 0

Reorder the terms:
4ab + a2 + -21b2 = 0

Solving
4ab + a2 + -21b2 = 0

Solving for variable 'a'.

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

Subproblem 1
Set the factor '(a + -3b)' equal to zero and attempt to solve:

Simplifying
a + -3b = 0

Solving
a + -3b = 0

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

Add '3b' to each side of the equation.
a + -3b + 3b = 0 + 3b

Combine like terms: -3b + 3b = 0
a + 0 = 0 + 3b
a = 0 + 3b
Remove the zero:
a = 3b

Simplifying
a = 3b
Subproblem 2
Set the factor '(a + 7b)' equal to zero and attempt to solve:

Simplifying
a + 7b = 0

Solving
a + 7b = 0

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

Add '-7b' to each side of the equation.
a + 7b + -7b = 0 + -7b

Combine like terms: 7b + -7b = 0
a + 0 = 0 + -7b
a = 0 + -7b
Remove the zero:
a = -7b

Simplifying
a = -7b
Solution
a = {3b, -7b}