If the surface area of a cone is given by the formula [tex]S=\pi\cdot l+\pi\cdot r^2,[/tex] then you have to express l in terms of S and r.
1. Express the whole expression [tex]\pi\cdot l:[/tex]
[tex]\pi\cdot l=S-\pi\cdot r^2.[/tex]
2. Divide the previous expression by [tex]\pi:[/tex]
[tex]l=\dfrac{S-\pi r^2}{\pi}=\dfrac{S}{\pi}-r^2.[/tex]
3. Since [tex]\pi\approx 3.14,[/tex] then
[tex]l=\dfrac{S}{3.14}-r^2.[/tex]
Answer: correct choice is C (here should be S not 5 as written)
