The scent of a certain air freshener evaporates at a rate proportional to the amount of the air freshener present. Half of the air freshener evaporates within $2$ hours of being sprayed. If the scent of the air freshener is undetectable once $80\%$ has evaporated, how long will the scent of the air freshener last?

Separate the variables of the following differential equation.

$ysi{n}^2\theta \frac{dy}{d\theta }=1$

Find the particular solution that satisfies the given initial condition

$(y^2+y)e^x{y}^{\prime }=y^3+e^x{y}^3;y\left(0\right)=1$

Find the general solution to the differential equation.

$\frac{dy}{dx}=y\sqrt{x}$

Find the particular solution that satisfies the given initial condition $\frac{dy}{dx}=\sin x\bullet \sec y,y\left(\frac{\pi }{2}\right)=\frac{\pi }{4}$.

$\$2,000$ is invested in an account that earns interest at a rate of $8.5\%$ and is compounded continuously. Find the particular solution that describes the growth of this account in dollars $A$ after $t$ years.  Hint: When interest is compounded continuously, it grows exponentially with a growth constant equivalent to the interest rate.

A pie is removed from an oven and its temperature is $175\text{℃}$ and placed into a refrigerator whose temperature is constantly $3\text{℃}$. After $1$ hour in the refrigerator, the pie is $90\text{℃}$. What is the temperature of the pie $4$ hours after being placed in the refrigerator?

Separate the variables of the following differential equation.

$ysi{n}^2\theta \frac{dy}{d\theta }=1$