a- 1≠0 a≠ 1

3a^2- 1=2 3a^2=3 a^2= 1 a = 1

a=- 1

12、y=20000+36000x+ 16000x^2

y =[20000( 1+x)-20000 x * 20%]( 1+x)

=20000( 1+0.8x)( 1+x)

=20000( 1+ 1.8x+0.8x^2)

=20000+36000x+ 16000x^2

13，y =-(x-3/2) 2+ 17/9 x = 3/2， 17/9； x & gt=3/2

y=-x^2+3x+2

=-[x^2-3x+(3/2)^2]+2+9/4

=-(x-3/2)^2+ 17/9

14、c=9

y=x^2-6x+c

=(x-3)^2+c-9

Vertex on the X axis: c-9=0

c=9

15、( 1)③ (2)① (3)④ (4)②

In this problem, when x= 1, the value of y is compared.

16、a & gt2

y=(a- 1)x^2-2x+ 1

δ& lt； 0

(-2)^2-4(a- 1)<； 0

4-4a+4 & lt； 0

4a> Ba

a & gt2