Let a and b be real numbers such that a + b = -1. Compute a^2 - b^2 + 2a.
See https://web2.0calc.com/questions/algebra_63536
a^2 - b^2 + 2a = (a + b)(a - b) + 2a
substitute a + b = -1
-1(a - b) + 2a = -a + b + 2a = a + b = -1.
