The height and the total surface area of a right circular

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The height and the total surface area of a right circular cylinder are 4 cm and 8π sq.cm. respectively. The radius of the base of cylinder is

Height of cylinder = 4 cm.
Total surface area = 2πr (r + h)
∴ 2πr (r + h) = 8π
⇒ r (r + 4) = 4
⇒ r² + 4r – 4 = 0

⇒ r =	- 4 ± √16 + 16
	2

=	- 4 ± √32
	2

= – 2 + 2√2
because r ≠ –2 – 2√2
Note : If ax² + bx + c = 0, then x

⇒ r =	- b ± √b² - 4ac
	2a