Question

in triangle abc D and e are midpoints of a b and ac is ad 3.5
cm is 4 cm is equal to 2.5 cm find the perimeter of triangle ABC

Answer 1

Dear Student,

In ∆ABC, since D and E are the mid point of AB and AC, thenDE = 12 BC  (Mid point theorem)⇒BC = 2×2.5 = 5 cmNow, AB = 2 AD = 7 cmAC = 2AE = 2×4 = 8 cmNow, perimeter of ∆ABC = AB + BC + CA = 7 + 5 + 8 = 20 cm

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Swagat Swargari answered this
1109 helpful votes in Math, Class IX

///this seems to be Class X question

We know that: line joining the mid-points of 2 sides of a triangle is parallel to the third side.
so, DE is parallel to BC   //as D and E are the mid-points of AB and AC

Now, in triangle ABC and ADE,
angle A = angle A (common)
angle ABC = angle ADE (corresponding angles)
angle ACB = angle AED (corresponding angles)

so triangle ABC similar to triangle ADE
or AC/AE = BC/DE
or 8/4 = BC/2.5   
as E is the mid-point of AC so AC = 2*AE = 2*4 = 8 cm or BC = 2*2.5 = 5 cm

so, perimeter of triangle ABC = AB + AC + BC
= 7 + 8 + 5 = 20 cm 

since D is the mid-point of AB so AB = 2*AD = 2*3.5 = 7 cm

Answer 2

Step-by-step explanation:

pls see the pic given above . Hope it helps you . Though I'm not quite sure about it.