task/29409747 --------------------
( ( 1 / (c²+3c+2) +2c/(c²+4c+3) +1 /(c²+5c+6) )*( (c-3)² + 12c ) /2
==========================
1.
( 1 / (c+1)(c+2) +2c / (c+1)(c+3) +1 / (c+2)(c+3) =
(c+3 +2c (c+2) + c+1 ) / ( c+1)(c+2)(c+3) = ( 2c²+6c +4 ) / ( c+1)(c+2)(c+3) =
2(c²+3c +2 ) /( c+1)(c+2)(c+3) = 2/ (c+3) .
2.
( (c-3)² + 12c ) /2 =(c² -6c +9 +12c) /2 =(c² +6c +9 ) /2 =(c+3)² /2
3.
( 2/ (c+3) ) * (c+3)² / 2 = c+3 .
Ответ : c +3