1 Mark each
(i) x2=5 is not a linear equation since the highest exponent of the variable is 2.
(ii) x+y=4 has two variables in it. So, it is not a linear equation.
(iii) x+6=9 is a linear equation in one variable.
(iv) x2+y2=9 has two variables in it, and the highest exponent is 2. So, it is not a linear equation.