A cone has radius 5x cm and a height 12x cm.A sphere has radius r cm.The cone has the same total surface area as the sphere.Show that r²=45÷2 x². (The curved surface area,A, of a cone with radius r and slant height l is A=πrl.) (The surface area,A, of a sphere with radius r is A=4πr².)
1 answer:
Answer:
r^2 = 45÷2 x^2
Step-by-step explanation:
Details of cone:
Radius(r) = 5x cm
Height(h) = 12x cm
Slant height(l) = √(12x^2 + 5x^2)
l = 13x cm
Total surface area of a cone (T. S. A) = πrl + πr²
T. S. A = π * 5x * 13x + π5x^2
T.S.A = π65x^2 + π5x^2
T.S.A = π65x^2 + π25x^2
T.S.A = 90πx^2 - - - - - (1)
Details of sphere:
Radius (r) = r cm
Total surface area = 4πr²
Total Surface area of sphere= 4πr²cm - - - (2)
Equating (1) and (2) to calculate r
4πr² = 90πx^2
r^2 = 90πx^2 / 4π
r^2 = 90π (x^2) / 4π
r^2 = 45/2 (x^2) ;
r^2 = 45÷2 x^2
Hence the proof
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