lo g 3 x + 5 ( 9 x 2 + 8 x + 8 ) > 2
Solve the inequality above for x .
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Why is 9x2+8x+8 >1? Whereas we know than the base and the no. Both shud always be greater than 0
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lo g 3 x + 5 ( 9 x 2 + 8 x + 8 ) = lo g ( 3 x + 5 ) lo g ( 9 x 2 + 8 x + 8 ) > 2
⇒ lo g ( 9 x 2 + 8 x + 8 ) 9 x 2 + 8 x + 8 9 x 2 + 8 x + 8 0 x > 2 lo g ( 3 x + 5 ) > ( 3 x + 5 ) 2 > 9 x 2 + 3 0 x + 2 5 > 2 2 x + 1 7 < − 2 2 1 7
We note that when lo g ( 3 x + 5 ) < 0 then lo g ( 3 x + 5 ) lo g ( 9 x 2 + 8 x + 8 ) < 0 > 2 . Therefore, for lo g ( 3 x + 5 ) lo g ( 9 x 2 + 8 x + 8 ) > 2
⇒ lo g ( 3 x + 5 ) > 0 ⇒ 3 x + 5 > 1 ⇒ x > − 3 4
Therefore, the answer: x ∈ ( − 3 4 , − 2 2 1 7 )
The graph below clearly shows the answer.