Question

当a的二次方+b的二次方=6时,求(3a的平方-2ab-b的平方)-(a的平方-2ab-3b的平方)的

值

Answer 1

(3a²-2ab-b²)-(a²-2ab-3b²)
=3a²-2ab-b²-a²+2ab+3b²
=3a²-a²-2ab+2ab-b²+3b²
=2a²+2b²
=2﹙a²+b²﹚
∵a²+b²=6
∴原式=2﹙a²+b²﹚=2×6=12