A5 A ladder is leaning against a vertical wall to a height of $9 \mathrm{~m}$. The top end of the ladder slides down by 1 $\mathrm{m}$, so that the bottom end of the ladder is $6 \mathrm{~m}$ away from the wall. How long is the ladder?
(A) $8 \mathrm{~m}$
(B) $8.5 \mathrm{~m}$
(C) $9 \mathrm{~m}$
(D) $9.5 \mathrm{~m}$
(E) $10 \mathrm{~m}$
A5 We use the Pythagorean theorem in a right-angled triangle, where $x$ is the length of the straight pipe we are looking for. Thus, $x^{2}=6^{2}+8^{2}$, from which we get that $x=10 \mathrm{~m}$.