[碎片化时间管理] [20240114]
[初中数学]
解:此题用对偶式方法巧解求值
(2a+3b)²=4a²+12ab+9b² ①
(3a-2b)²=9a²一12ab+4b² ②
①+②,得
(2a+3b)²+(3a-2b)²=13a²+13b²
=13×5
=65
(2a+3b)²+(3a-2b)²=65
(2a+3b)²=65-(3a-2b)²
当(3a-2b)²=0时
(2a+3b)²=65
即,2a+3b=✓65
[碎片化时间管理] [20240114]
[初中数学]
解:此题用对偶式方法巧解求值
(2a+3b)²=4a²+12ab+9b² ①
(3a-2b)²=9a²一12ab+4b² ②
①+②,得
(2a+3b)²+(3a-2b)²=13a²+13b²
=13×5
=65
(2a+3b)²+(3a-2b)²=65
(2a+3b)²=65-(3a-2b)²
当(3a-2b)²=0时
(2a+3b)²=65
即,2a+3b=✓65