最大角為A,A>60°,則sinA=
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2 |
1 |
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由三角形兩邊之和大于第三邊知,x+(x-2)>x+2,即x>4,
由預(yù)先定理得:cosA=
x2+(x?2)2?(x+2)2 |
2x(x?2) |
x2?8x |
2x(x?2) |
x?8 |
2x?4 |
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即2(x-8)=-2x+4,解得:x=5.
∴三角形的三邊分別為3,5,7.
該三角形的面積為:
1 |
2 |
1 |
2 |
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2 |
15
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4 |
故選:B.
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2 |
15 |
4 |
15
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4 |
21
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4 |
35
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4 |
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2 |
1 |
2 |
x2+(x?2)2?(x+2)2 |
2x(x?2) |
x2?8x |
2x(x?2) |
x?8 |
2x?4 |
1 |
2 |
1 |
2 |
1 |
2 |
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2 |
15
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4 |