SOLUTION: I'm having trouble understanding this statement: If triangle ABC is similar to triangle DEF AB=4, BC=8, AC=11 DE=10, EF=20, DF=n Solve for n. I know the perimeter of a triang

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Question 206886: I'm having trouble understanding this statement: If triangle ABC is similar to triangle DEF
AB=4, BC=8, AC=11
DE=10, EF=20, DF=n Solve for n.
I know the perimeter of a triangle is P=a+b+c but I can't seem to solve for n. It's like there are 2 unknowns. Can you please let me know what I am doing wrong. Thank-you!

Found 2 solutions by jim_thompson5910, Edwin McCravy:
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
If ABC is similar to DEF, then the corresponding sides form a ratio. In other words, the ratio of AB to DE is the same as the ratio of BC to EF. Similarly, the ratio of BC to EF is equal to the ratio of AC to DF.


What this means is AB%2FDE=BC%2FEF and if you plug in the given lengths, you get 4%2F10=8%2F20 (which is indeed true).

Furthermore, this means that BC%2FEF=AC%2FDF and plugging in the given values gets us 8%2F20=11%2Fn. So all you need to do from here is solve for 'n'


Note: because all the ratios are equal, we can also solve the equation 4%2F10=11%2Fn and get the same answer.


Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
Edwin's solution:
I'm having trouble understanding this statement: If triangle ABC is similar to triangle DEF
AB=4, BC=8, AC=11
DE=10, EF=20, DF=n Solve for n.
I know the perimeter of a triangle is P=a+b+c but I can't seem to solve for n. It's like there are 2 unknowns. Can you please let me know what I am doing wrong. Thank-you!




You're supposed to do this by proportions:

      (DF is to AC) as (DE is to AB) as (EF is to BC)

Write the proportion as an equation:

            DF%2FAC+=+DE%2FAB+=+EF%2FBC

Substitute their lengths:

            n%2F11+=+10%2F4+=+20%2F8

Reducing the fractions:

            n%2F11+=+5%2F2+=+5%2F2

            n%2F11+=+5%2F2

Cross multiply:

            2n=55

            n=55%2F2=27%261%2F2

Edwin