ABC is an isosceles triangle inscribed in a circle of radius r. If AB=AC&h is the altitude from A to BC and P be the perimeter of ABC, then limh→0ΔP3 equals (where Δ is the area of traingle)
A
132r3
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B
164r3
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C
1128r3
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D
None of these
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Solution
The correct option is C1128r3 DC=√r2−(h−r)2=√r2−(h2+r2−2hr)=√2hr−h2Area=12×2DC×h⇒h√2hr−h2AC=√DC2+h2=√2hr−h2+h2=√2hrP=2AC+BC=2√2hr+2√2hr−h2⇒2√h(√2r+√2r−h)P3=8h√h(√2r+√2r−h)3△P3=h√2h−h28h√h(√2r+√2r−h)3limh→0⇒h√h√2−h8h√h(√2r+√2r−h)3⇒√2−h8(√2r+√2r−h)3⇒18×√2(2√2r)3⇒18×√216√2r3⇒1128r3