The threshold voltage of an n-channel MOSFET can be increased by

The following system of equations
$${{x_1} + {x_2} + {x_3} = 3}$$
$${{x_1} - {x_3} = 0}$$
$${{x_1} - {x_2} + {x_3} = 1}$$ has

The rank of $$\left( {m \times n} \right)$$ matrix $$\left( {m < n} \right)$$ cannot be more then

The function $$y = {x^2} + {{250} \over x}$$ at $$x=5$$ attains