Question on: WAEC Mathematics - 2001
The diagram shows a triangular prism of length 7cm. The right - angled triangle PQR is a cross section of the prism |PR| = 5cm and |RQ| = 3cm. What is the volume of the prism?
A
28cm2
B
42cm2
C
70cm2
D
84cm2
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Correct Option: B
Volume of prism = Area x height
In \(\Delta\) RQP, QR\(^2\) + QP\(^2\) = RP\(^2\)
3\(^2\) + QP\(^2\) = 5\(^2\)
QP\(^2} = 5\(^2\) - 3\(^2\)
QP = \(\sqrt{16}\)
= 4 cmÂ
\(\therefore\) Area = \(\frac{1}{2} \times base \times height\)
= \(\frac{1}{2} \times 3 \times 4\)
= 6 cm\(^2\)
Volume = 6 x 7
= 42 cm\(^3\)
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