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(1)已知x+y=3,xy=2,求(x-y)2,x2+y2的值.(2)已知(a+b)2=7,(a-b)2=5,求①a2+b2的值;②求a
(1)已知x+y=3,xy=2,求(x-y)2,x2+y2的值.(2)已知(a+b)2=7,(a-b)2=5,求①a2+b2的值;②求ab的值....
(1)已知x+y=3,xy=2,求(x-y)2,x2+y2的值.(2)已知(a+b)2=7,(a-b)2=5,求①a2+b2的值;②求ab的值.
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(1)∵x+y=3,xy=2,
∴(x-y)2=(x+y)2-4xy=32-4×2=9-8=1;
x2+y2=(x+y)2-2xy=32-2×2=9-4=5;
(2)①∵(a+b)2=7,(a-b)2=5,
∴a2+b2=
=
=6;
②ab=
=
=
.
∴(x-y)2=(x+y)2-4xy=32-4×2=9-8=1;
x2+y2=(x+y)2-2xy=32-2×2=9-4=5;
(2)①∵(a+b)2=7,(a-b)2=5,
∴a2+b2=
(a+b)2+(a?b)2 |
2 |
7+5 |
2 |
②ab=
(a+b)2?(a?b)2 |
4 |
7?5 |
4 |
1 |
2 |
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