Question:
If ∆ABC ∼ ∆EDF and ∆ABC is not similar to ∆DEF, then which of the following is not true?
(a) BC ⋅ EF = AC ⋅ FD
(b) AB ⋅ EF = AC ⋅ DE
(c) BC ⋅ DE = AB ⋅ EF
(d) BC ⋅ DE = AB ⋅ FD
Solution:
(c) BC ⋅ DE = AB ⋅ EF
∆ABC ∼ ∆EDF
Therefore,
$\frac{A B}{D E}=\frac{A C}{E F}=\frac{B C}{D F}$
$\Rightarrow B C \cdot D E \neq A B \cdot E F$