(2-1)(1+a)+1=15

Solution for (2-1)(1+a)+1=15 equation:

Simplifying
(2 + -1)(1 + a) + 1 = 15

Combine like terms: 2 + -1 = 1
(1)(1 + a) + 1 = 15
(1 * 1 + a * 1) + 1 = 15
(1 + 1a) + 1 = 15

Reorder the terms:
1 + 1 + 1a = 15

Combine like terms: 1 + 1 = 2
2 + 1a = 15

Solving
2 + 1a = 15

Solving for variable 'a'.

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

Add '-2' to each side of the equation.
2 + -2 + 1a = 15 + -2

Combine like terms: 2 + -2 = 0
0 + 1a = 15 + -2
1a = 15 + -2

Combine like terms: 15 + -2 = 13
1a = 13

Divide each side by '1'.
a = 13

Simplifying
a = 13