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The solution of 7x+12x−9<4\frac{7x+12}{x-9} < 4; ≠9 \neq 9 is:

Solution

✅ Correct Option: 3

Move all terms to one side of the inequality:

7x+12x−9−4<0\frac{7x+12}{x-9} - 4 < 0


Express as a single fraction with common denominator:

7x+12x−9−4(x−9)x−9<0\frac{7x+12}{x-9} - \frac{4(x-9)}{x-9} < 0

7x+12−4(x−9)x−9<0\frac{7x+12 - 4(x-9)}{x-9} < 0


Simplify the numerator:

7x+12−4x+36x−9<0\frac{7x+12 - 4x + 36}{x-9} < 0

3x+48x−9<0\frac{3x + 48}{x-9} < 0

Factor out 3 from the numerator:

3(x+16)x−9<0\frac{3(x + 16)}{x-9} < 0


Find the critical points where the expression equals zero or is undefined:

Numerator = 0: x+16=0x + 16 = 0 → x=−16x = -16

Denominator = 0: x−9=0x - 9 = 0 → x=9x = 9 (undefined)


Test the sign in each interval:

IntervalTest valueSign of (x+16)(x+16)Sign of (x−9)(x-9)Sign of fraction
x<−16x < -16x=−20x = -20(−)(-)(−)(-)(+)(+)
−16<x<9-16 < x < 9x=0x = 0(+)(+)(−)(-)(−)(-)
x>9x > 9x=10x = 10(+)(+)(+)(+)(+)(+)

The fraction is negative when −16<x<9-16 < x < 9.

Note that x=9x = 9 is excluded since the expression is undefined there.

The solution is {x:−16<x<9;x∈R}\boxed{\{x: -16 < x < 9; x \in \mathbb{R}\}}

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