# in triangle ABC , angle A =900 , AB = 5cm and AC = 12cm . if AD is perpendicular to BC , then AD = ?de options r ....a. 13/2b. 60/13c. 13/60d. 2root15 / 13plz answer...and also justify...plz!!

b)60 / 13

in this A = 900 ...........

In triangle ABC ....

AB2 + AC2 = BC2

---> BC = root(144 + 25) = root(169) = 13 cm ......

In triangle ADC and triangle ABC .....

angle BAC = angle ADC = 900 ....

angle ACB = angle DCA ... [common angle] ...

Hence ....

triangle ADC ~ triangle ABC [A-A postulate] .....

As both traingles r similar ...

then according to sides theorem :-

BC / AC =  AB / AD

----> 13 / 12 =  5 / AD

----> AD = 60 / 13 .......(ans) ...

Hope this helps !!!

• 8

thank u sooo much...i am out of thumbs up ...i wil giv thumbs up 2 morrow...

srry..  :(

• -3

yeh sab thumbzz down kaun de raha hai ..??

• 0

Hi!
@   Silent_SIlver correctly answered the question.

Good effort!
Keep writing!!!

Note:
The last seventh line of the answer posted by Silent_SIlver needs a correction. It should be
triangle ADC ~ triangle BAC [A-A postulate] ..... instead of triangle ADC ~ triangle ABC [A-A postulate] .....

It is because of the similarity of two triangles should also be expressed symbolically, using correct correspondence of their vertices.

Cheers!

• -2
What are you looking for?