The problem gives two quadratic functions $f(x) = 2ax^2 + (2a+1)x + a$ and $g(x) = -ax^2 - x - 1$. (1) We need to find the expression for $f(x) - g(x)$ in the form $Jax^2 + K(a+L)x + a + M$ and determine the values of $J, K, L, M$. (2) Using the result from (1), we need to find the range of values of $a$ for which the two parabolas $y=f(x)$ and $y=g(x)$ have no intersection points. We are given options for the range of $a$.

AlgebraQuadratic EquationsDiscriminantInequalitiesParabolas
2025/6/10

1. Problem Description

The problem gives two quadratic functions f(x)=2ax2+(2a+1)x+af(x) = 2ax^2 + (2a+1)x + a and g(x)=ax2x1g(x) = -ax^2 - x - 1.
(1) We need to find the expression for f(x)g(x)f(x) - g(x) in the form Jax2+K(a+L)x+a+MJax^2 + K(a+L)x + a + M and determine the values of J,K,L,MJ, K, L, M.
(2) Using the result from (1), we need to find the range of values of aa for which the two parabolas y=f(x)y=f(x) and y=g(x)y=g(x) have no intersection points. We are given options for the range of aa.

2. Solution Steps

(1) Calculate f(x)g(x)f(x) - g(x):
f(x)g(x)=(2ax2+(2a+1)x+a)(ax2x1)f(x) - g(x) = (2ax^2 + (2a+1)x + a) - (-ax^2 - x - 1)
f(x)g(x)=2ax2+(2a+1)x+a+ax2+x+1f(x) - g(x) = 2ax^2 + (2a+1)x + a + ax^2 + x + 1
f(x)g(x)=(2a+a)x2+(2a+1+1)x+(a+1)f(x) - g(x) = (2a+a)x^2 + (2a+1+1)x + (a+1)
f(x)g(x)=3ax2+(2a+2)x+a+1f(x) - g(x) = 3ax^2 + (2a+2)x + a+1
f(x)g(x)=3ax2+2(a+1)x+a+1f(x) - g(x) = 3ax^2 + 2(a+1)x + a+1
Comparing this with the given form Jax2+K(a+L)x+a+MJax^2 + K(a+L)x + a + M, we have:
J=3J=3, K=2K=2, L=1L=1, M=1M=1.
So, f(x)g(x)=3ax2+2(a+1)x+a+1f(x) - g(x) = 3ax^2 + 2(a+1)x + a+1
(2) The two parabolas y=f(x)y=f(x) and y=g(x)y=g(x) have no intersection points if and only if the equation f(x)=g(x)f(x) = g(x) has no real solutions. This is equivalent to f(x)g(x)=0f(x) - g(x) = 0 having no real solutions.
Therefore, we need to find the values of aa for which the quadratic equation 3ax2+2(a+1)x+(a+1)=03ax^2 + 2(a+1)x + (a+1) = 0 has no real solutions.
If a=0a=0, the equation becomes 2x+1=02x+1=0, which has a solution x=1/2x=-1/2. So aa cannot be

0. If $a \ne 0$, the discriminant of the quadratic equation must be negative:

D=b24ac<0D = b^2 - 4ac < 0
D=(2(a+1))24(3a)(a+1)<0D = (2(a+1))^2 - 4(3a)(a+1) < 0
4(a+1)212a(a+1)<04(a+1)^2 - 12a(a+1) < 0
4(a+1)(a+13a)<04(a+1)(a+1 - 3a) < 0
4(a+1)(12a)<04(a+1)(1-2a) < 0
(a+1)(12a)<0(a+1)(1-2a) < 0
This inequality holds if either
(i) a+1>0a+1>0 and 12a<01-2a<0, which means a>1a>-1 and 2a>12a>1, so a>1a>-1 and a>1/2a>1/2. Thus a>1/2a > 1/2.
(ii) a+1<0a+1<0 and 12a>01-2a>0, which means a<1a<-1 and 2a<12a<1, so a<1a<-1 and a<1/2a<1/2. Thus a<1a < -1.
Therefore, the range of values of aa is a<1a<-1 or a>1/2a>1/2.

3. Final Answer

The range of aa is a<1a<-1 or a>1/2a>1/2, which corresponds to option (2).
J=3J = 3
K=2K = 2
L=1L = 1
M=1M = 1
Final Answer: a<1,1/2<aa<-1, 1/2<a
Option (2) is the correct one.

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