Hello sharma ,

Here the function is f(x)=2x-kx+5

in the interval [1,2]

First we are equalling the function f(x)=0

After substitute the first interval , then f(1)=2(1)-k(1)+5=0

solve the above equation you will get k=7

After substitute the second interval in the function f(2)= 2(2)-k(2)+5=0

solve the above equation you will get k=9/2 =4.5

the interval for k is [4.5,7]

I hope this will help for you.

THANK YOU.