Firstly, altitude is a line which passes through a vertex of a triangle, and is at right angles to the opposite side.

__General Info:__We know that each side of the triangle will be 6 (18/3 = 6). In this case, a is the first leg, b is the second leg and c is the hypothenuse. Pythagoras: C^{2}= a^{2}+ b^{2}__How do we work out this problem?____The altitude = a (variable) b (second leg) = 6/2 = 3 c (hypothenuse) = 6 c__^{2}= a^{2}+ b^{2 }(make a the subject of the formula) c^{2 }- b^{2 }= a^{2 }+ b^{2}- b^{2}(subtract b from both sides) a^{2}= c^{2 }- b^{2 }(simplify) a^{2}= 6^{2}- 3^{2}(plug in the values) a^{2 }= 36 - 9 = 27 (simplify) √a^{2}= √27 (eliminate the exponent) a = 5.196152423 FINAL ANSWER: The altitude of this triangle will be 5.196152423