Let, y = (x² + 1) cos x

We have to find dy/dx

As we can observe that y is a product of two functions say u and v where,

u = x² + 1 and v = cos x

∴ y = uv

As we know that to find the derivative of product of two function we apply product rule of differentiation.

By product rule, we have –

…equation 1

As, u = x² + 1

∴

⇒ …equation 2 {∵ }

As, v = cos x

…equation 3 {∵ }

∴ from equation 1, we can find dy/dx

∴

⇒ {using equation 2 & 3}

Hence,