Can a triangle have all angles less than $60^{\circ}$? Give reason for your answer.

$\angle ACD$ is an exterior angle of $\Delta ABC$. If $AB = AC$ and $\angle B = 70^{\circ}$,then $\angle ACD = \dots$ (in $^{\circ}$)

Bisectors of the angles $B$ and $C$ of an isosceles triangle with $AB = AC$ intersect each other at $O$. $BO$ is produced to a point $M$. Prove that $\angle MOC = \angle ABC$.

Is it possible to construct a triangle with lengths of its sides as $9 \, cm$,$7 \, cm$,and $17 \, cm$? Give reason for your answer.

$D$ is any point on side $AC$ of a $\triangle ABC$ with $AB = AC$. Show that $CD < BD$.

If one angle of a triangle is equal to the sum of the other two angles,then the triangle is