21=a-(-13)

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Solution for 21=a-(-13) equation:


Simplifying
21 = a + -1(-13)

Multiply -1 * -13
21 = a + 13

Reorder the terms:
21 = 13 + a

Solving
21 = 13 + a

Solving for variable 'a'.

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

Add '-1a' to each side of the equation.
21 + -1a = 13 + a + -1a

Combine like terms: a + -1a = 0
21 + -1a = 13 + 0
21 + -1a = 13

Add '-21' to each side of the equation.
21 + -21 + -1a = 13 + -21

Combine like terms: 21 + -21 = 0
0 + -1a = 13 + -21
-1a = 13 + -21

Combine like terms: 13 + -21 = -8
-1a = -8

Divide each side by '-1'.
a = 8

Simplifying
a = 8

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