ABC is a triangle right angled at B with AB=8cm and BC=6cm. It is made to revolve about its side BC. What is the approximate total surface area of the cone so formed? (Take π=‌
In right angled triangle ABC given that, ‌AB=8cm ‌BC=6cm
When the triangle is revolved about its side BC, the height of the cone so formed, h=6cm the radius of the cone so formed, r=8cm Therefore, total surface area of the cone formed =πr2+πrl . . . (i) In △ABC, AC2=AB2+BC2 I2=82+62 I2=100 ⇒I=10cm From Eq. (i), we have Total surface area of the cone =πr(r+l) ‌‌=‌
22
7
×8×(8+10) ‌‌=‌
22×8×18
7
‌‌=‌
3168
7
‌‌≈452cm2 Hence, the required approximate total surface area of the cone formed is 452cm2.