Skip to main contentSkip to solution

A triangle ABC is formed with AB = AC = 50 cm and BC = 80 cm. Then, the sum of the lengths, in cm, of all three altitudes of the triangle ABC is

Entered answer:

Solution

✅ Correct Answer: 126

Given an isosceles triangle ABC with AB=AC=50AB = AC = 50 cm and BC=80BC = 80 cm.


Since the triangle is isosceles with AB=ACAB = AC, the altitude from AA to BCBC bisects BCBC at midpoint MM.

BM=MC=802=40BM = MC = \dfrac{80}{2} = 40 cm

Using Pythagoras theorem in triangle ABMABM:

h12+402=502h_1^2 + 40^2 = 50^2

h12=2500−1600=900h_1^2 = 2500 - 1600 = 900

h1=30h_1 = 30 cm


Area of triangle ABCABC:

=12×BC×h1= \dfrac{1}{2} \times BC \times h_1

=12×80×30= \dfrac{1}{2} \times 80 \times 30

=1200= 1200 cm2^2


The area remains the same regardless of which side is chosen as the base. Using ACAC as the base with h2h_2 as the corresponding altitude:

1200=12×50×h21200 = \dfrac{1}{2} \times 50 \times h_2

h2=240050h_2 = \dfrac{2400}{50}

h2=48h_2 = 48 cm


Similarly, using ABAB as the base with h3h_3 as the corresponding altitude:

1200=12×50×h31200 = \dfrac{1}{2} \times 50 \times h_3

h3=240050h_3 = \dfrac{2400}{50}

h3=48h_3 = 48 cm

Since AB=ACAB = AC, the altitudes h2h_2 and h3h_3 are equal.


Sum of all three altitudes:

=h1+h2+h3= h_1 + h_2 + h_3

=30+48+48= 30 + 48 + 48

=126= 126 cm

Keyboard Shortcuts

  • Left arrow: Previous question
  • Right arrow: Next question
  • S key: Jump to solution
  • Q key: Jump to question