The three sides of a triangle are given which one of the following is not a right angle?

In the following figure, $\mathrm{AD}$ is the external bisector of $\angle \mathrm{EAC},$ and it intersects $\mathrm{BC}$ produced to $\mathrm{D}.$ If $\mathrm{AB}=12 \mathrm{cm},\mathrm{AC}=8 \mathrm{cm}$ and $\mathrm{BC}=4 \mathrm{cm},$ find $\mathrm{CD}.$

In the given figure, $\mathrm{AB}=\mathrm{BC}$ and $\angle \mathrm{BAC}=15°,\mathrm{AB}=10,$ $\mathrm{cm}.$ Find the area of $∆\mathrm{ABC}.$

In the given figure, if $\frac{\mathrm{DE}}{\mathrm{BC}}=\frac{2}{3}$ and if $\mathrm{AE}=10 \mathrm{cm}.$ Find $\mathrm{AB}$