若(a+2)²+丨b+1丨=0 ,求5ab² -｛2a²b-[3ab²-(4ab²-2a²b)]｝的值?
若(a+2)²+丨b+1丨=0 ,
(a+2)²>=0;丨b+1丨>=0;
所以(a+2)²=0,A=-2;丨b+1丨=0,b=-1;
5ab² -｛2a²b-[3ab²-(4ab²-2a²b)]｝
=5ab² -｛2a²b-[3ab²-4ab²+2a²b]｝
=5ab² -｛2a²b-[-ab²+2a²b]｝
=5ab² -｛2a²b+ab²-2a²b｝
=5ab² -ab²
=4ab²
=4(-2)(-1)²
=-8