The problem asks us to find the range of values for the constant $a$ such that the equation $4^x - a \cdot 2^{x+1} + a^2 + a - 6 = 0$ has two distinct real solutions for $x$.

AlgebraQuadratic EquationsInequalitiesExponentsRoots of EquationsDiscriminant
2025/6/27

1. Problem Description

The problem asks us to find the range of values for the constant aa such that the equation 4xa2x+1+a2+a6=04^x - a \cdot 2^{x+1} + a^2 + a - 6 = 0 has two distinct real solutions for xx.

2. Solution Steps

First, rewrite the given equation:
4xa2x+1+a2+a6=04^x - a \cdot 2^{x+1} + a^2 + a - 6 = 0
(2x)22a2x+a2+a6=0(2^x)^2 - 2a \cdot 2^x + a^2 + a - 6 = 0
Let t=2xt = 2^x. Since xx is a real number, t>0t > 0.
Then the equation becomes
t22at+a2+a6=0t^2 - 2at + a^2 + a - 6 = 0
For the original equation to have two distinct real solutions for xx, the quadratic equation in tt must have two distinct positive solutions for tt.
Let f(t)=t22at+a2+a6f(t) = t^2 - 2at + a^2 + a - 6.
For f(t)=0f(t) = 0 to have two distinct positive solutions, we need the following conditions to be satisfied:

1. The discriminant must be positive: $D > 0$

2. The sum of the roots must be positive: $t_1 + t_2 > 0$

3. The product of the roots must be positive: $t_1 t_2 > 0$

D=(2a)24(1)(a2+a6)=4a24a24a+24=4a+24D = (-2a)^2 - 4(1)(a^2 + a - 6) = 4a^2 - 4a^2 - 4a + 24 = -4a + 24
D>0    4a+24>0    4a<24    a<6D > 0 \implies -4a + 24 > 0 \implies 4a < 24 \implies a < 6
The sum of the roots is t1+t2=(2a)1=2at_1 + t_2 = \frac{-(-2a)}{1} = 2a.
2a>0    a>02a > 0 \implies a > 0
The product of the roots is t1t2=a2+a61=a2+a6t_1 t_2 = \frac{a^2 + a - 6}{1} = a^2 + a - 6.
a2+a6>0    (a+3)(a2)>0a^2 + a - 6 > 0 \implies (a+3)(a-2) > 0
This implies a<3a < -3 or a>2a > 2.
Combining these conditions:

1. $a < 6$

2. $a > 0$

3. $a < -3$ or $a > 2$

Since a>0a > 0, the condition a<3a < -3 is not possible.
Therefore, we need a>0a > 0, a<6a < 6, and a>2a > 2.
So the solution is 2<a<62 < a < 6.

3. Final Answer

2<a<62 < a < 6

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