Question

please answer even if you know any one also
will surely mark as the brainliest if I get all the answer clearly with all steps and everything
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Answer 1

Answer:

GIVEN,

height of cone:- 21cm

slant height. :- 28cm

as we know that ,

AC²= AB²+BC² [ by Pythagoras theorem]

28² = 21²+ BC²

784= 441 + BC²

BC²= 748-441

BC = √307 = 17.52

Area of base = πr²

= 22/7 x 17.52 x 17.52

= 964.70 cm²

Answer 2

                                                                                                           

$question 12 :$

$height of cone , h = 21 cm$

$slant height , l = 28 cm$

$let the radius of cone = r$

$therefore ,$

$l^2 = r^2 + h^2$

$r^2 = l^2 - h^2$

$r =$  $\sqrt{28^2 - 21^2}$

$r = \sqrt{784 - 441}$

$r = \sqrt{343} = 7\sqrt{7} cm$

$area of base = \pi r^2$

$22/7 * (7\sqrt{7} )^2$ $= 22 * 49 = 1078 cm^2$

                                                                                                          

$question 13 :$

$radius of wall , r = 2.1 cm$

$density of ball , d = 8.9 g / cm^3$

$therefore ,$

$volume of ball , V = \frac{4}{3} \pi r^3$

$V = \frac{4}{3} * 22/7 * 2.1 * 2.1 * 2.1 = 38.808 cm^3$

$mass of the ball = volume * density$

$m = 8.9 * 38.808 = 345.39 g$