Question

The surface area of a cone is given by the formula S = πl + πr2. Solve the formula for l.

Answer 1

If the surface area of a cone is given by the formula $S=\pi\cdot l+\pi\cdot r^2,$ then you have to express l in terms of S and r.

1. Express the whole expression $\pi\cdot l:$

$\pi\cdot l=S-\pi\cdot r^2.$

2. Divide the previous expression by $\pi:$

$l=\dfrac{S-\pi r^2}{\pi}=\dfrac{S}{\pi}-r^2.$

3. Since $\pi\approx 3.14,$ then

$l=\dfrac{S}{3.14}-r^2.$

Answer: correct choice is C (here should be S not 5 as written)

Answer 2

L = S/π - r^2 .......
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