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Q.

Find the complete solution set for the inequation  18+x < 2-x?


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a

[−18,−2]

b

(−∞,−2)∪(7,∞)

c

(−18,−2)∪(7,∞)

d

[−18,−2) 

answer is D.

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Detailed Solution

According to the problem, we need to find the complete solution set of the inequation 18+x<2-x.
Let us first find the value for which the given inequation is defined.
We know that for a function g(x)  is defined only if g(x)≥0.
So, we have 18+x ≥ 0.
⇒x ≥ −18.
⇒x∈[−18,∞) ---(1).
We know that the 2−x is a polynomial and we can see that all of its values should be greater than zero as we know that the value of the 18+x    ≥0.
So, we have 2−x > 0.
⇒x < 2.
⇒x∈(−∞,2) ---(2).
The common interval of x for which the given inequation is defined will be the intersection of the values of x obtained in equations (1) and (2).
So, the inequation 18+x < 2−x is defined on x∈[−18,2) ---(3).
Now, let us find the solution set for the inequation 18+x  < 2−x.
⇒(18+x)2 < (2−x)2.
⇒18+x < 4−4x+x2.
⇒x2−5x−14 > 0.
⇒x2−7x+2x−14 > 0.
⇒x(x−7)+2(x−7) > 0.
⇒(x+2)(x−7) > 0.
⇒(x−(−2))(x−7) > 0 ---(4).
We know that if the inequality is defined as (x−a)(x−b) > 0 and a < b, then the solution set of the inequality is x < a or x > b. Using this we get the solution set for inequality in equation (4) as x < −2 or x > 7.
From equation (3), we remove the values of x which were not satisfying the interval x < −2 or x > 7 to get the complete solution set.
So, we get the solution set for the inequality as x∈[−18,−2).
So, the correct answer is “Option 4”.
 
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