This is a Test of Mathematics Solution Subjective 66 (from ISI Entrance). The book, Test of Mathematics at 10+2 Level is Published by East West Press. This problem book is indispensable for the preparation of I.S.I. B.Stat and B.Math Entrance.

Also visit: I.S.I. & C.M.I. Entrance Course of Cheenta

## Problem

If c is a real number with 0 < c < 1, then show that the values taken by the function y = , as x varies over real numbers, range over all real numbers.

## Solution

y =

or + 4yx + 3cy = + 2x + c

or (y-1) + (4y-2)x + 3cy – c = 0

Now if we can show that the discriminant for all y then for all real y there exist a real x.

Now, discriminant is – 4(y-1)(3cy-c)

We need to show – 4(y-1)(3cy-c) > 0 for any 0 < c < 1. (16-12c) – (16-16c)y + (4-4c) > 0.

This is parabola opening upword.

Now if its discriminant < 0 then this equation is always > 0.

So this is equivalent to prove

– 4 (16-12c)(4-4c) < 0.

or – (4-3c)(1-c) < 0

or -C < 0

Now given 1>c>0 so <c

or -c < 0

*Conclusion:* So for 1>c>0 y =

Range over all real number when x varies over all real number.