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 area of the cross-section?
A.
4cm2
B.
6cm2
C.
15cm2
D.
20cm2
Correct answer is B
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 cm
\(\therefore\) Area = \(\frac{1}{2} \times base \times height\)
= \(\frac{1}{2} \times 3 \times 4\)
= 6 cm\(^2\)