1-(3-a)(2+5)=1

Solution for 1-(3-a)(2+5)=1 equation:

Simplifying
1 + -1(3 + -1a)(2 + 5) = 1

Combine like terms: 2 + 5 = 7
1 + -1(3 + -1a)(7) = 1

Reorder the terms for easier multiplication:
1 + -1 * 7(3 + -1a) = 1

Multiply -1 * 7
1 + -7(3 + -1a) = 1
1 + (3 * -7 + -1a * -7) = 1
1 + (-21 + 7a) = 1

Combine like terms: 1 + -21 = -20
-20 + 7a = 1

Solving
-20 + 7a = 1

Solving for variable 'a'.

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

Add '20' to each side of the equation.
-20 + 20 + 7a = 1 + 20

Combine like terms: -20 + 20 = 0
0 + 7a = 1 + 20
7a = 1 + 20

Combine like terms: 1 + 20 = 21
7a = 21

Divide each side by '7'.
a = 3

Simplifying
a = 3