(a-b)^2的差
a+b=3,ab=-10,a-b=?
解 :
(a-b)²
=a²+b²-2ab
=(a+b)²-4ab
=3²-4X(-10)
=9+40
=49
∴ a-b=±√(a-b)²=±√49=±7
(a-b)²=a²-2ab+b²=(a+b)²-4ab=9+40=49
a-b=±7
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a+b=3,ab=-10,a-b=?
解 :
(a-b)²
=a²+b²-2ab
=(a+b)²-4ab
=3²-4X(-10)
=9+40
=49
∴ a-b=±√(a-b)²=±√49=±7
(a-b)²=a²-2ab+b²=(a+b)²-4ab=9+40=49
a-b=±7