Answer:
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Correct answer: 1 Mark
Reason: 1 Mark
Steps: 2 Marks
From the figure, we can see that
BO is perpendicular to AC and AO = OC
$\because$ BO is cutting the base into half and is also perpendicular to it.
$\therefore$ BO is acting both as an altitude and median.
An altitude acts as a median only in an Equilateral or Isosceles triangle with AB and BC being equal in length.
For the triangle ABC,
Sum of all angles = 180${}^o$
Or, $\angle A$ + $\angle B$ + $\angle C$ = 180${}^o$
Or, $\angle A$ + $\angle C$ + 60${}^o$ = 180
Or, 2$\angle A$ = 180${}^o$ - 60${}^o$ ($\because$ angles opposite to equal sides are equal)
Or, $\angle A$ = $\frac{{120}^o}{2}$ = 60${}^o$
$\because$ $\angle A$ = $\angle B$ = $\angle C$ = 60${}^o$
$\therefore$ The above triangle is an Equilateral triangle.