Question

a d is perpendicular to BC

Answer 1

as AB and AC are equal

Answer 2

In Triangle ABD & ACD

angleBAD= angleCAD

AB= AC

angleABD=angleACD

Therefore

Triangle ABD congruent to Triangle ACD

therefore angle ADB is equal to angle ADC

angle ADB + angle ADC = 180 degree

(LINEAR PAIR OF ANGLES)

2 angle ADC = 180 degree

angle ADC = angle ADB =90 degree

THEREFORE AD PERPENDICULAR TO BC

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