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  • The total surface area of a cone whose radius is frac{r}{2} and slant height 2l is (A) 2\pi r( l+r ) (B) pi r ( l+frac{r}{4})(C) pi r ( l+r )

The total surface area of a cone whose radius is \frac{r}{2} and slant height 2l is

(A) 2\pi r\left ( l+r \right )

(B) \pi r\left ( l+\frac{r}{4} \right )

(C) \pi r\left ( l+r \right )

(D) 2\pi r l

Answers (1)

Answer (B)

We know that total surface area of cone is given as =\pi .R\; L+\pi R^{2}

Where R is the radius of its base and L is the slant height.

Now, it is given that :

Radius of cone \left ( R \right )=\frac{r}{2}

Slant height (L) =2l

So total surface area =\pi \left ( \frac{r}{2} \right )\left ( 2l \right )+\pi \left ( \frac{r}{2} \right )^{2}

                                  =\pi r l+\frac{\pi r^{2}}{4}

                                  =\pi r\left ( l+\frac{r}{4} \right )

So, option (B) is the correct answer.

 

Posted by

infoexpert23

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