1、-20
2、3
3、[- 1, 1 1]
4、3
5、 1/5
6、0.4
7、22
8、 1:8
9, (2, -9) or (-2, 15)
10、m & ltn
1 1、4
12、( 1)(2)
13,2 * (root number 7)-5
14、-9
15、( 1)、2
(2)、32
(3) Omission
16, omitted
17 、( 1)an = 2 * n-7； Sn=n*n-6*n
(2) there is no m.
18, (1) y =+-2 * (square root of 6) *(x-4)
(2)p:(-3/2， 13/2)； (5/2,-2)
19, (1)h A = radical sign [mA*mB/(mA+ 12)(mB+5)]
H b = radical sign [mA*mB/(mA+3)(mB+20)]
(2) Ma = 12, and when MB = 20, H A = h B = radical sign (2/5).
(3) does not exist
20 、( 1)a = & lt； 1
(2) when a >; F(x)min=2*a*a when =0.
When a<0 f(x)min=2*a/3.
(3)① when 0 < a< (root number 2)/2 hours
X & gt=[a+ radical sign (3-a*a)]/3
2 when a>= (root number 2)/2
x∈(a，+∞)
③ When (the square root of 6) /2
X = < [a+radical sign (3-a*a)]/3
④ When a =
x∈(a，+∞)