Answer:
? = -2
Step-by-step explanation:
a + b = -2
so, now we need to find all (a + b) combinations in the large expression.
for example, we know
a = -2 - b
or b = -2 - a
and then
-b = 2 + a
but also
3b = -6 - 3a
so that
a - b = a + 2 + a = 2a + 2
therefore
(a + b)(a - b) = a² - b² = -2(2a + 2) = -4a - 4
(-4a - 4 - 12b - 36)/(-4a - 4 - 6a - 6b) =
(-4(a + 3b) - 40)/(-4a - 4 - 6(a + b)) =
(-4(a - 6 - 3a) - 40)/(-4a - 4 - 6×-2) =
(-4(-2a - 6) - 40)/(-4a + 8) =
(8a + 24 - 40)/(-4a + 8) = (8a - 16)/(-4a + 8) =
-2×(-4a + 8)/(-4a + 8) = -2
