UPSKILL MATH PLUS

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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.