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The set of values of xx which satisfy the inequality 0.7(2x23x+4)<0.3430.7^{(2x^2 - 3x + 4)} < 0.343 is

Solution

Correct Option: 4
Solution figure for IPMAT Indore 2019 MCQ question 10 (Algebra)

Concept:

(0.7)a<(0.7)3(0.7)^a < (0.7)^3

Since 0.7<10.7 < 1, the inequality flips when comparing exponents, so a>3a > 3

Why? A base less than 11 raised to a higher power gives a smaller result. For example, (0.7)4=0.2401<0.343=(0.7)3(0.7)^4 = 0.2401 < 0.343 = (0.7)^3. So for (0.7)a(0.7)^a to be less than (0.7)3(0.7)^3, we need a>3a > 3.


Since 0.343=(0.7)30.343 = (0.7)^3, the inequality becomes:

(0.7)2x23x+4<(0.7)3(0.7)^{2x^2 - 3x + 4} < (0.7)^3

Flipping the inequality (base <1< 1):

2x23x+4>32x^2 - 3x + 4 > 3

2x23x+1>02x^2 - 3x + 1 > 0


Factorizing:

2x22xx+1>02x^2 - 2x - x + 1 > 0

2x(x1)1(x1)>02x(x - 1) - 1(x - 1) > 0

(2x1)(x1)>0(2x - 1)(x - 1) > 0

Roots are x=12x = \dfrac{1}{2} and x=1x = 1


We need the product to be positive, so we check the signs across the number line:

RegionSign of (2x1)(2x-1)Sign of (x1)(x-1)Product
x<12x < \dfrac{1}{2}--++
12<x<1\dfrac{1}{2} < x < 1++--
x>1x > 1++++++

x(, 12)(1, )\boxed{x \in \left(-\infty,\ \dfrac{1}{2}\right) \cup \left(1,\ \infty\right)}

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