lo g 2 ( 1 + x 4 ) + lo g 2 ( 1 − x + 4 4 ) = 2 lo g 2 ( x − 1 2 − 1 )
How many real solutions does the above equation have?
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@Rishabh Cool B. how much marks are you getting in mains??? and your classmates.....my analysis is this year paper was quite on a simpler side and easy as comp. to last year....how was your paper
Why did you delete your comment?
Stunniing solution, nice work!
Isn't 1-(4/(x+4)) equal to x/(x+4), not (x+4)/x? Then wouldn't the first step in the solution be incorrect?
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lo g ( x + 4 x ) = lo g ( x x + 4 ) − 1 = − lo g ( x x + 4 )
And minus sign is removed when we square it to get : lo g 2 ( x x + 4 )
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Thanks for the clarification. That problem was cleverly made.
Shit made a mistake at the end rest was correct.
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Some simplification gives: 2 lo g 2 ( x x + 4 ) = 2 lo g 2 ( x − 1 3 − x ) ( ∗ ∗ ) ⟹ lo g ( x x + 4 ) = ± lo g ( x − 1 3 − x ) = lo g ( x − 1 3 − x ) ± 1 ⟹ x x + 4 = x − 1 3 − x and x x + 4 = 3 − x x − 1
⟹ x 2 − 2 = 0 and x 2 − 6 = 0
⟹ x = 2 , 6 ∈ ( 1 , 3 ) (See below) i.e 2 values. ∴ the correct option is x 2 − 7 x + 1 0 = 0 since 2 is a root of this equation only.
Since domain of lo g function is R + we get x x + 4 > 0 and x − 1 3 − x > 0 . Solving we get x ∈ ( 1 , 3 ) .