Is the area of triangle ACB the same as triangle AXB?  Click "animate horizontal" and observe the area of ACB as point C moves towards X.

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Is the height of triangle ACB the same as triangle AXB?

What happens to the area when the height or base changes?
Drag any point to a new position. Tilt the base if you have to.

Observe the fact that:
AREA OF TRIANGLE depends only on the BASE and HEIGHT
or, mathematically,
1/2 x base x height