16 9
17 12
18 (15,10)(11,7)(7,4)(3,1)
19 n(n+1)/2 กับ 3n(n+1)/2
20 34.4736
21 (2x-1)(x-5)(x+1)(x+2)
22 $\sqrt{5}-1,-\sqrt{5}-1,2,3 $
23$ \Pi \sqrt{3} /6$
24$ \sqrt{3} $
25 ข 10403/60
26 $\sqrt{65} $
27 27,28
28 312.5
29 12000, 3000 หรือ 4000
30 m=3 n=12
31 690
32 75
33 104
34 120 40
35 2.4
36 3
37 132
38 45
39 \frac{mn}{m+n}
40 $(2,3),(-2,3), (\sqrt{21} ,-2),(-\sqrt{21} ,-2)$
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