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Question 1 : The real root of the equation 26x + 23x+2 - 21 = 0 is
Given equation - 26x + 23x+2 - 21 = 0
The idea is to convert the above equation to a quadratic one.
So, 26x =
Let y =
Now, 26x + 23x+2 - 21 = 0 can be rewritten as + 22.23x - 21 = 0
y2 + 4y - 21 = 0
Solving the above quadratic equation,
(y + 7) (y - 3) = 0
So, y = -7 or +3
y = => y should always be positive
Therefore, y = -7 is not a valid solution. So, only y = +3 exists.
Taking log on both sides,
x = , which is the real solution to the given equation
The question is "The real root of the equation 26x + 23x+2 - 21 = 0 is"
Choice A is the correct answer.
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