The exterior angle $\mathrm{ACD}$ of a $∆\mathrm{ABC}$ is $105°$. If $\angle \mathrm{B}=70°$, find $\angle \mathrm{A}$. Is $\angle \mathrm{ACD}>\angle \mathrm{A}$ ?
Find $\angle \mathrm{ACB}$ also.

 Study the $9$ triangles in the following figure: Name the right triangles.

 Study the $9$ triangles in the following figure:
 Name the obtuse triangles.

 Study the $9$ triangles in the following figure:
 Name the acute triangles.

O is a point in the interior of $∆\mathrm{ABC}$. State which of the following statements are true or false. Give reasons in support of your answer.
$\mathrm{OA}+\mathrm{OB}>\mathrm{AB}$
 

 O is a point in the interior of $∆\mathrm{ABC}$. State which of the following statements are true or false. Give reasons in support of your answer.
$\mathrm{OB}+\mathrm{OC}>\mathrm{BC}$
 

O is a point in the interior of $∆\mathrm{ABC}$. State which of the following statements are true or false. Give reasons in support of your answer.

$\mathrm{OA}+\mathrm{OC}=\mathrm{AC}$

Which of the following figures is a quadrilateral?