Total surface area of a cylinder of height 5.5cm is 198cm2 find its ra

1.	Total surface area of a cylinder of height 5.5cm is 198cm2 find its radius
Answer» $Let \: r \:and \: h \:are \: radius \:and \:height \\of \: a \: cylinder \: respectively$ $h = 5.5 \:cm$ $\boxed { \pink { TSA \: of \: a\: cylinder = 2\pi r(r+h) }}$ $Total \: Surface\:Area \: of \:the \: cylinder \\= 198 \:cm^{2} \:(given)$ $\implies 2\pi r(r+h) = 198$ $\implies 2 \times \frac{22}{7} \times r(r+5.5)= 198$ $\implies 2r(r + 5.5) = 198 \times \frac{7}{22}$ $\implies 2r^{2} + 11r = 63$ $\implies 2r^{2} + 11r - 63 = 0$ /* Splitting the middle TERM,we GET / $\implies 2r^{2} + 18r - 7r - 63 = 0$ $\implies 2r( r + 9 ) - 7( r + 9 ) = 0$ $\implies ( r + 9 )( 2r - 7 ) = 0$ $\implies ( r + 9 ) = 0 \: Or \: 2r - 7 = 0$ $\implies r = -9\: Or \: 2r = 7$ $\implies r = -9\: Or \: r = \frac{7}{2}$ / r should not be NEGATIVE */ Therefore., $\red { Radius \:of \:the \: cylinder }$ $\green { = \frac{7}{2} \:cm = 3.5 \:cm }$ •••♪