The image contains a geometric problem involving triangles and angles. Here's a breakdown of what we see:

Given Information:

• $\angle A$, $\angle B$, $\angle C$ are all less than 90° (acute angles).
• $BD \perp AC$ (BD is perpendicular to AC).
• $CE \perp AB$ (CE is perpendicular to AB).

You are asked to prove two things:

1. $\triangle ADE \sim \triangle ABC$ (that $\triangle ADE$ is similar to $\triangle ABC$).
2. $BH \times BD + CH \times CE = BC^2$ (a relation involving the product of line segments).

Approach for part a) $\triangle ADE \sim \triangle ABC$:

To prove that two triangles are similar, we need to demonstrate that they have corresponding angles equal and corresponding sides in proportion.

1. Equal angles:

   • Since $BD \perp AC$ and $CE \perp AB$, triangles $ABD$ and $ACE$ are right-angled triangles.
   • Therefore, they share a common angle at $A$, making them similar by AA similarity criterion.

2. Corresponding sides proportionality:

   • From the diagram and right-angled triangles, we can find the ratios of corresponding sides.

Approach for part b) $BH \times BD + CH \times CE = BC^2$:

This equation resembles a common result in Euclidean geometry that relates the areas of smaller triangles or segments of a triangle to the area of the larger triangle.

This could be proved using the Pythagorean theorem or by using properties of the projections $BD$ and $CE$ in relation to the hypotenuse $BC$.

Would you like further details on how to prove these two parts step by step?

Here are 5 follow-up questions related to the image:

1. What is the significance of proving triangle similarity in this problem?
2. How does the Pythagorean theorem help in proving part (b)?
3. Could you describe the role of perpendiculars in determining geometric relations in triangles?
4. What other geometric properties might be used to relate the segments in part (b)?
5. How would this problem change if one of the angles were obtuse?

Tip: Remember that proving triangle similarity can often simplify the relationships between line segments. It helps you directly compare corresponding sides.