Another Inequality

Algebra Level 3

( x 1 ) ( x + 4 ) ( x + 2 ) ( x 2 9 ) ( x + 8 ) < 0 \dfrac {(x-1)(x+4)(x+2)}{(x^2-9)(x+8)}<0

Find the number of integers x x that satisfy the inequality above.

5 3 7 4 6

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1 solution

Md Zuhair
Jan 29, 2017

Here , in this equation ( x 1 ) ( x + 4 ) ( x + 2 ) ( x 2 9 ) ( x + 8 ) < 0 \dfrac {(x-1)(x+4)(x+2)}{(x^2-9)(x+8)}<0 = ( x 1 ) ( x + 4 ) ( x + 2 ) ( x 3 ) ( x + 3 ) ( x + 8 ) < 0 \dfrac {(x-1)(x+4)(x+2)}{(x-3)(x+3)(x+8)}<0

Multiplying ( x 3 ) ( x + 3 ) ( x + 8 ) (x-3)(x+3)(x+8) in Numerator And Denominator, We get

( x 1 ) ( x + 4 ) ( x + 2 ) ( x 3 ) ( x + 3 ) ( x + 8 ) ( x 3 ) 2 ( x + 3 ) 2 ( x + 8 ) 2 < 0 \dfrac {(x-1)(x+4)(x+2)(x-3)(x+3)(x+8)}{(x-3)^2(x+3)^2(x+8)^2}<0

Hence As Denominator is > 0 > 0 ( As all are squares)

We get

( x 1 ) ( x + 4 ) ( x + 2 ) ( x 3 ) ( x + 3 ) ( x + 8 ) < 0 (x-1)(x+4)(x+2)(x-3)(x+3)(x+8)<0

Hence,

By wavy Curve Method,

It looks something like this,

Now as we have to find for < 0 < 0 , We will take the negetive part

hence x ϵ x \epsilon (- 8 , -4) U (-3 , -2) U (1, 3))

Hence now see, x must be integers

So Between 8 -8 and 4 -4 , we get 5 , 6 , 7 -5, -6, -7 ----> 3 \boxed{3} Solutions

For 3 -3 to 2 -2 , 0 \boxed{0} solutions as No integer is there in between

and Between 1 1 to 3 3 we have 2 2 , So 1 \boxed{1} solutions

Hence Total Solutions = 3 + 1 + 0 3+ 1 + 0 = 4 \boxed{4}

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