(1)已知(a+b)²=11,(a-b)=9.则ab的值是_______.(2)(-3m-4n)²(3)已知a+b=3,ab=-12,求a²-ab+b²的值(4)已知a+b=5,ab=12,求2(a²+b²)的值
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(1)已知(a+b)²=11,(a-b)=9.则ab的值是_______.(2)(-3m-4n)²(3)已知a+b=3,ab=-12,求a²-ab+b²的值(4)已知a+b=5,ab=12,求2(a²+b²)的值
(1)已知(a+b)²=11,(a-b)=9.则ab的值是_______.
(2)(-3m-4n)²
(3)已知a+b=3,ab=-12,求a²-ab+b²的值
(4)已知a+b=5,ab=12,求2(a²+b²)的值
(1)已知(a+b)²=11,(a-b)=9.则ab的值是_______.(2)(-3m-4n)²(3)已知a+b=3,ab=-12,求a²-ab+b²的值(4)已知a+b=5,ab=12,求2(a²+b²)的值
解
(a+b)²=11
a²+2ab+b²=11 ①
(a-b)²=9——这个吧?
a²-2ab+b²=9 ②
①-②得:4ab=2,∴ab=1/2
(-3m-4n)²
=(3m+4n)²
=9m²+24mn+16n²
a²-ab+b²
=(a+b)²-3ab
=3²-3×(-12)
=9+36
=45
2(a²+b²)
=2[(a+b)²-2ab]
=2(5²-2×12)
=2(25-24)
=2
(1)已知(a+b)²=11,(a-b)²=9.则ab的值是_______.
ab=1/4[(a+b)²-(a-b)²]
=1/4×(11-9)
=1/2
(2)(-3m-4n)²
=(3m+4n)²
=9m²+24mn+16n²
(3)已知a+b=3,ab=-1...
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(1)已知(a+b)²=11,(a-b)²=9.则ab的值是_______.
ab=1/4[(a+b)²-(a-b)²]
=1/4×(11-9)
=1/2
(2)(-3m-4n)²
=(3m+4n)²
=9m²+24mn+16n²
(3)已知a+b=3,ab=-12,求a²-ab+b²的值
a²-ab+b²
=a²+2ab+b²-ab
=(a+b)²-ab
=3²-(-12)
=9+12
=21
(4)已知a+b=5,ab=12,求2(a²+b²)的值
2(a²+b²)
=2[(a+b)²-2ab]
=2[5²-2×12]
=2×(25-24)、
=2×1
=2
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1,ab=0.5
2,原式=9m²+24mn+16n²
3,(a+b)²=a²+2ab+b²=9
3ab=-36
∴a²-ab+b²=45
4,(a+b)²=a²+2ab+b²=25
2ab=24 ∴a²+b²=1
2(a²+b²)=2
(1)已知(a+b)²=11,(a-b)²=9.则ab的值是_______.
ab=1/4[(a+b)²-(a-b)²]
=1/4×(11-9)
=1/2
(2)(-3m-4n)²
=(3m+4n)²
=9m²+24mn+16n²
(3)已知a+b=3,ab=-1...
全部展开
(1)已知(a+b)²=11,(a-b)²=9.则ab的值是_______.
ab=1/4[(a+b)²-(a-b)²]
=1/4×(11-9)
=1/2
(2)(-3m-4n)²
=(3m+4n)²
=9m²+24mn+16n²
(3)已知a+b=3,ab=-12,求a²-ab+b²的值
a²-ab+b²
=a²+2ab+b²-ab
=(a+b)²-ab
=3²-(-12)
=9+12
=21
(4)已知a+b=5,ab=12,求2(a²+b²)的值
2(a²+b²)
=2[(a+b)²-2ab]
=2[5²-2×12]
=2×(25-24)、
=2×1
=2希望我的回答可以帮助到你,也祝你的学习进步,如果满意的话就请你采纳我的答案!谢谢
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