“Stationary waves” are so called because in them

The equation of a stationary wave is $y = 0.8 \cos \left( \frac{\pi x}{20} \right) \sin (200 \pi t)$,where $x$ is in $cm$ and $t$ is in $sec$. The separation between consecutive nodes will be .... $cm$.

In a standing wave on a string $:-$

Two progressive waves $Y_{1} = \sin 2\pi(\frac{t}{0.4} - \frac{x}{4})$ and $Y_{2} = \sin 2\pi(\frac{t}{0.4} + \frac{x}{4})$ superpose to form a standing wave. $x, Y_{1}$ and $Y_{2}$ are in $SI$ units. The amplitude of the particle at $x = 0.5 \ m$ is: (Given: $\sin 45^{\circ} = \cos 45^{\circ} = \frac{1}{\sqrt{2}}$)

Consider the three waves $z_1, z_2$ and $z_3$ as $z_1 = A \sin(kx - \omega t)$,$z_2 = A \sin(kx + \omega t)$ and $z_3 = A \sin(ky - \omega t)$. Which of the following represents a standing wave?

For a stationary wave represented by the equation $y = 0.15 \sin(5x) \cos(300t) \, \text{m}$,what is the wavelength of the wave (in $, \text{m}$)?