Question 1139377
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The given triangle, with side lengths 3, 4, and 5, is a right triangle.<br>
Let the triangle be ABC, with the right angle at C; AC=3, BC=4; AB=5.  The altitude to the hypotenuse, CD, divides triangle ABC into two smaller right triangles that are both similar to triangle ABC.  You can find the lengths of AD and BD using those similar triangles.<br>
Using the similar triangles ADC and ABD,<br>
{{{AD/AC = AC/AB}}}
{{{AD/3 = 3/5}}}
{{{AD = 9/5 = 1.8}}}<br>
Then of course BD is 5-1.8=3.2; but you could also find that using similar triangles CDB and ACB:<br>
{{{DB/CB = BC/AC}}}
{{{DB/4 = 4/5}}}
{{{DB = 16/5 = 3.2}}}