D, E and F are the points on sides BC, CA and AB respectively of ∆ABC such that AD bisects ∠A, BE bisects ∠B and CF bisects ∠C. If AB = 5 cm, BC = 8 cm and CA = 4 cm, determine AF, CE and BD.
It is given that $A B=5 \mathrm{~cm}, B C=8 \mathrm{~cm}$ and $C A=4 \mathrm{~cm}$.
We have to find $A F, C E$ and $B D$.
Since $A D$ is bisector of $\angle A$
So $\frac{A B}{A C}=\frac{B D}{C D}$
Then,
54=BDBC-BD⇒54=BD8-BD⇒40-5BD=4BD⇒9BD=40
So, $B D=\frac{40}{9}$
Since $B E$ is the bisector of $\angle B$.
So,
ABBC=AEEC⇒ABBC=AC-ECEC
$\frac{5}{8}=\frac{4-C E}{C E}$
$5 C E=32-8 C E$
$5 C E+8 C E=32$
$13 C E=32$
So
$C E=\frac{32}{13} \mathrm{~cm}$
Now since $C F$ is the bisector of $\angle C$
So $\frac{B C}{C A}=\frac{B F}{A F}$
$\frac{8}{4}=\frac{A B-A F}{A F}$
$\frac{8}{4}=\frac{5-A F}{A F}$
$8 A F=20-4 A F$
$12 A F=20$
So
$3 A F=5 \mathrm{~cm}$
$A F=\frac{5}{3} \mathrm{~cm}$
Hence $A F=\frac{5}{3} \mathrm{~cm}$
$C E=\frac{32}{13} \mathrm{~cm}$
And $B D=\frac{40}{9} \mathrm{~cm}$