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If x and y are real numbers such that x > 1 and y < −1,
then which of the following inequalities must be true?
A. x/y> 1
B. |s|^2 > |y|
C. x/3− 5 > y/3 − 5
D. x^2 + 1 > y^2 + 1
E. x^(−2) > y^(−2)

Respuesta :

[tex]x > 1\ \wedge\ y < -1\\\\A.\ \frac{x}{y} > 1-FALSE;example:x=2;\ y=-2\ then\\L=\frac{2}{-2}=-1;R=1;\ L < R\\\\B.\ |x|^2 > |y|-FALSE;example:x=2;\ y=-6\ then\\L=|2|^2=2^2=4;R=|-6|=6;\ L < R\\\\C.\ \frac{x}{3}-5 > \frac{y}{3}-5-TRUE;\frac{x}{3}-5 > \frac{y}{3}-5\to\frac{x}{3} > \frac{y}{3}\to x > y[/tex]

[tex]D.\ x^2+1 > y^2+1-FALSE;example:x=2;\ y=-3\ then\\L=2^2+1=4+1=5;R=(-3)^2+1=9+1=10;L < R\\\\E.\ x^{-2} > y^{-2}-FALSE;example:x=3;\ y=-2\ then\\L=3^{-2}=\frac{1}{9};R=(-2)^{-2}=\frac{1}{4};\ L < R[/tex]

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