Solve the inequality $\frac{t-1}{4t+5} < \frac{t-3}{4t-3}$.

AlgebraInequalitiesRational InequalitiesInterval AnalysisAlgebraic Manipulation
2025/5/25

1. Problem Description

Solve the inequality t14t+5<t34t3\frac{t-1}{4t+5} < \frac{t-3}{4t-3}.

2. Solution Steps

First, subtract t34t3\frac{t-3}{4t-3} from both sides to get:
t14t+5t34t3<0\frac{t-1}{4t+5} - \frac{t-3}{4t-3} < 0
Next, find a common denominator and combine the fractions:
(t1)(4t3)(t3)(4t+5)(4t+5)(4t3)<0\frac{(t-1)(4t-3) - (t-3)(4t+5)}{(4t+5)(4t-3)} < 0
Expand the numerator:
4t23t4t+3(4t2+5t12t15)(4t+5)(4t3)<0\frac{4t^2 -3t -4t +3 - (4t^2 +5t -12t -15)}{(4t+5)(4t-3)} < 0
4t27t+3(4t27t15)(4t+5)(4t3)<0\frac{4t^2 -7t +3 - (4t^2 -7t -15)}{(4t+5)(4t-3)} < 0
Simplify the numerator:
4t27t+34t2+7t+15(4t+5)(4t3)<0\frac{4t^2 -7t +3 - 4t^2 +7t +15}{(4t+5)(4t-3)} < 0
18(4t+5)(4t3)<0\frac{18}{(4t+5)(4t-3)} < 0
Since the numerator is positive (18 > 0), the inequality is satisfied when the denominator is negative:
(4t+5)(4t3)<0(4t+5)(4t-3) < 0
Find the critical points by setting each factor to zero:
4t+5=04t=5t=544t+5 = 0 \Rightarrow 4t = -5 \Rightarrow t = -\frac{5}{4}
4t3=04t=3t=344t-3 = 0 \Rightarrow 4t = 3 \Rightarrow t = \frac{3}{4}
Now, test the intervals determined by these critical points:
Interval 1: t<54t < -\frac{5}{4}
Let t=2t = -2. Then (4(2)+5)(4(2)3)=(8+5)(83)=(3)(11)=33>0(4(-2)+5)(4(-2)-3) = (-8+5)(-8-3) = (-3)(-11) = 33 > 0.
Interval 2: 54<t<34-\frac{5}{4} < t < \frac{3}{4}
Let t=0t = 0. Then (4(0)+5)(4(0)3)=(5)(3)=15<0(4(0)+5)(4(0)-3) = (5)(-3) = -15 < 0.
Interval 3: t>34t > \frac{3}{4}
Let t=1t = 1. Then (4(1)+5)(4(1)3)=(4+5)(43)=(9)(1)=9>0(4(1)+5)(4(1)-3) = (4+5)(4-3) = (9)(1) = 9 > 0.
The inequality is satisfied when 54<t<34-\frac{5}{4} < t < \frac{3}{4}.

3. Final Answer

54<t<34-\frac{5}{4} < t < \frac{3}{4}