Question : The 'IBM-DOS' is a

Option 1: single user operating system

Option 2: multiuser operating system

Option 3: batch operating system

Option 4: time-sharing operating system

Question : Which of the following is not an operating system?

Option 1: Android

Option 2: Vista

Option 3: iOS

Option 4: Opera

Question : If $a^{2}=b+c,b^{2}=c+a,c^{2}=a+b$, the value of $3\left (\frac{1}{a+1}+\frac{1}{b+1}+\frac{1}{c+1}\right)$ is:

Option 1: $1$

Option 2: $\frac{1}{3}$

Option 3: $3$

Option 4: $4$

Question : If $\frac{a^2}{b+c}=\frac{b^2}{c+a}=\frac{c^2}{a+b}=1$, then $\frac{1}{1+a}+\frac{1}{1+b}+\frac{1}{1+c}$ is:

Option 1: 1

Option 2: 2

Option 3: 3

Option 4: 4

Question : If $a, b, c$ are real numbers and $a^{2}+b^{2}+c^{2}=2(a-b-c)-3,$ then the value of $a+b+c$ is:

Option 1: –1

Option 2: 1

Option 3: 3

Option 4: 0