Aspire Faculty ID #16440 · Topic: NIMCET 2009 · Just now
NIMCET 2009

Number of distinct integer values of $a$ satisfying $2^{2a} - 3(2^{a+2}) + 25 = 0$ is:

Solution

Rewrite: $2^{2a} - 12\cdot 2^a + 25 = 0$ 
Let $t = 2^a$ (positive). 
Equation becomes: $t^2 - 12t + 25 = 0$ 
$t = \dfrac{12 \pm \sqrt{44}}{2} = 6 \pm \sqrt{11}$ 
We need $t = 2^a$, a power of 2. 
Check if $6 + \sqrt{11}$ or $6 - \sqrt{11}$ is a power of 2. 
 Values: $6 + \sqrt{11} \approx 9.316$ → not power of 2 
$6 - \sqrt{11} \approx 2.684$ → not power of 2 No integer $a$ exists.

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