Question 824277
Normally the order of the vertices used to name a triangle is not important. But when a statement about similar (or congruent) triangles is made, the order is meaning full.<br>
So "triangle ABC is similar to triangle DEF" tells us more than just the fact that the two triangles are similar. The first letters in the names correspond to each other (so A corresponds to D), the second letters correspond (B corresponds to E) and the third letters correspond (C corresponds to F).<br>
This also helps us figure out which sides correspond to which sides. AB corresponds to DE, BC corresponds to EF and AC corresponds to DF.<br>
Since corresponding sides of similar triangles are proportional, then various ratios of the corresponding sides are equal. Since we're interested in AB we will start with a ratio of AB to its corresponding side from the other triangle:
{{{AB/DE}}}
Now we will write a couple more ratios of corresponding sides:
{{{BC/EF}}}
{{{AC/DF}}}<br>
Because of the proportionality, all three of these ratios are going to be equal. So
{{{AB/DE = BC/EF}}}
Multiplying each side of this by DE we get:
{{{AB = DE*(BC/EF)}}}
This is one of the two possible answers.<br>
Also,
{{{AB/DE = AC/DF}}}
Again we multiply by DE:
{{{AB = DE*(AC/DF)}}}
This is the other possible answer.