Question

√(a+b)²-√9b² , a<0 , b<0

Answer 1

$\sqrt{(a+b)^2}-\sqrt{9b^2}\\\\|a+b|-3|b|, \quad a<0\quad b<0\quad \rightarrow\quad a+b<0\\\\-(a+b)-(-3b)\\\\-a-b+3b\\\\\boxed{-a+2b}$