Q. Let y=x+2x2+4x+5, where x=−2.Prove that if x∈R then y cannot take values between −2 and 2 .
Simplify Expression for y: Let's start by simplifying the expression for y by performing polynomial division or factoring, if possible.y=x+2x2+4x+5We can try to factor the numerator, but since the roots of x2+4x+5 are complex, we cannot factor it over the real numbers. Therefore, we will perform polynomial division.
Perform Polynomial Division: Perform polynomial division of the numerator by the denominator.(x2+4x+5)÷(x+2) gives us x+2 with a remainder of 1.So, y=x+2+(x+2)1
Analyze Expression y: Now, let's analyze the expression y=x+2+x+21. We know that x cannot be −2, so the term x+21 is always defined. For y to be between −2 and 2, the following inequality must be true: −2<x+2+x+21<2
Subtract 2 from Inequality: Subtract 2 from all parts of the inequality to isolate the fraction on one side.−4<x+x+21<0
Consider Left Part of Inequality: Now, let's consider the two parts of the inequality separately.First, let's look at the left part: −4<x+(x+2)1.For x>−2, the term (x+2)1 is positive, and thus x+(x+2)1 is always greater than x. Since x can be any real number greater than −2, there will always be values of x for which x+(x+2)1 is greater than −4.
Consider Right Part of Inequality: Now, let's look at the right part of the inequality: x+(x+2)1<0. For x>−2, the term (x+2)1 is positive, and thus x+(x+2)1 is always greater than x. For x+(x+2)1 to be less than 0, x would have to be negative and its absolute value would have to be greater than (x+2)1. However, as x approaches x>−20 from the right, (x+2)1 becomes arbitrarily large, so there is no real number x for which x+(x+2)1 is less than 0.
Conclusion: Since there is no real number x for which x+x+21 is less than 0, the original inequality −2<x+2+x+21<2 cannot be satisfied for any real x. Therefore, y cannot take values between −2 and 2 for any real x.