(a)
In the diagram, < RTS = 28^\circ, < VRM = 46^\circ, MQ is a tangent to the circle VRSTU at the point R. Find < VUS.
(b) A cylinder tin, 7cm high, is closed at one end. If its total surface area is 462\(cm^{2}\), calculate its radius. [Take \(\pi = \frac{22}{7}\)].
Verified Correct Answer: .
Step-by-Step Mathematical Solution
(a)
In the diagram above, \(\alpha = 28^\circ\) (angles in alternate segment)
\(46^\circ + \beta + \alpha = 180^\circ\) (angles on a straight line)
\(46^\circ + \beta + 28^\circ = 74^\circ + \beta = 180^\circ\)
\(\beta = 180^\circ - 74^\circ = 106^\circ\)
\(x + \beta = 180^\circ\) (opposite angles of a cyclic quadrilateral)
\(x + 106^\circ = 180^\circ\)
\(x = 180^\circ - 106^\circ = 74^\circ\)
Hence, < VUS = 74^\circ.
(b) Total surface area = curved surface area + area of closed end
= \(2\pi rh + \pi r^{2}\)
= \(\pi r(2h + r)\)
\(462 = \frac{22r}{7}((2 \times 7) + r)\)
\(\frac{462 \times 7}{22} = r(14 + r)\)
\(147 = 14r + r^{2}\)
\(r^{2} + 14r - 147 = 0\)
\(r^{2} - 7r + 21r - 147 = 0\)
\(r(r - 7) + 21(r - 7) = 0\)
\((r + 21)(r - 7) = 0\)
\(r = \text{-21 or 7}\)
The radius cannot be negative, therefore, r = 7 cm.
Source: Myschool Past Questions Archive (Record #52450)