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Total surface area of a cone is 616 sq.cm. If the slant height of the cone is three times the radius of its base, find its slant height. - Geometry

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प्रश्न

Total surface area of a cone is 616 sq.cm. If the slant height of the cone is three times the radius of its base, find its slant height.

बेरीज

उत्तर

Let the radius of base and slant height of the cone be r cm and l cm, respectively.

Slant height of the cone = 3 × Radius of the cone         ...(Given)

∴ l = 3r

Total surface area of the cone = 616 cm2

∴ πr (r + l) = 616 cm2

⇒ `22/7 xx r xx (r + 3r)` = 616

⇒ `22/7 xx r xx 4r` = 616

⇒ `88/7` r2 = 616

⇒ r2 = ` [616  xx 7]/88`

⇒ r2 = 49

⇒ r = `sqrt 49` = 7cm

∴ Slant height of the cone, l = 3r = 3 × 7 = 21 cm

Thus, the slant height of the cone is 21 cm.

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पाठ 9: Surface Area and Volume - Problem Set 9 [पृष्ठ १२३]

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बालभारती Geometry (Mathematics 2) [English] 9 Standard Maharashtra State Board
पाठ 9 Surface Area and Volume
Problem Set 9 | Q 7. | पृष्ठ १२३
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