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Answer variants:
\(CY\) is perpendicular to \(AB\)
CPCT
altitudes
perpendicular line segment
two
\(\triangle ACY\)
\(\angle AXB = \angle AYC\)
\(BX\)
\(ACY\)
63.svg
 
Prove that the altitudes are \(BX\) and \(CY\) are equal if triangle \(ABC\) is isosceles with \(AB = AC\).
 
Proof:
 
It is given that \(BX\) and \(CY\) are 
of triangle \(ABC\).
 
An altitude is a 
An altitude is a perpendicular line segment drawn through the vertex of the triangle to the opposite side.
 
Here, \(CY\) is an altitude of \(AB\), and 
is an altitude of \(AC\).
 
Hence, 
and \(BX\) is perpendicular to \(AC\).
 
To prove that the altitudes are equal, let us consider 
and \(\triangle ABX\).
 
Here, \(AB = AC\) [Given]
  
Also, 
as the altitudes meet the sides at right angles.
 
Also, \(\angle A\) is common to both triangles 
and \(ABX\).
 
Here, 
corresponding pairs of angles and one corresponding pair of sides are equal.
 
Thus by  congruence criterion, \(\triangle ACY \cong \triangle ABX\).
 
Since \(\triangle ACY \cong \triangle ABX\), and by 
the altitudes \(CY\) and \(BX\) are equal.