Which of the following relationships between the acceleration a and the displacement $x$ of a particle involve simple harmonic motion?
(a) $a=0.7 x$
(b) $\mathbf{a}=-\mathbf{2 0 0} \mathrm{x}^{2}$

Condition of SHM is stated below,

Acceleration is directly proportional to negative of displacement of particle.

If ‘ $\mathrm{a}$ ‘ is the acceleration,

$\mathrm{x}$ is the displacement

Then, for Simple Harmonic Motion,

$\mathrm{a}=-\mathrm{kx}$ where $\mathrm{k}$ is constant

(a) $a=0.7 x$

This is not in the form of $a=-k x$

So, it is not SHM

(b) $a=-200 x^{2}$

Clearly we can see, it is not SHM