The function is .

Let the tangent point as .

Apply derivative on each side with respect to .

Slope of the tangent is derivative of the function at the given point. 

At : 

.

Point-slope form of line equation :  .

Substitute point  and slope  in the above equation.

Above tangent line passes through origin.

Therefore,

Thus, the tangent point is .

Substitute  in .

Therefore, tangent line equation is .

Graph:

Tangent point is .

Tangent line equation is .

.