Let $ABC$ be a triangle and $h_a,h_b,h_c$ the length of the heights.
(a) Find similar triangles at which it holds that $ah_a=bh_b$.
(b) Use (a) to show : Is $A'B'C'$ a second triangle and $h_a,h_b,h_c$ are again the length of the heights of this triangle, so these triangles are congruent.
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For (a) do we have to give two specific triangles, i.e. give the negth of the sides? Or what exactly is asked?
For part (a), yes, we have to find two similar triangles for which $ah_a=bh_b$ holds.
Draw $h_a$ and $h_b$ inside $\triangle ABC$. $h_a \cap BC \in D$. $h_b \cap CA \in E$. With simple angle chasing, $$\triangle ADC \sim \triangle BEC$$