SOLUTION: The trapezoid shown is divided into four triangles by its diagonals. The area of two triangles are indicated(9 and 25). What is the area of the whole trapezoid? <pre> Note: Ima

Algebra ->  Polygons -> SOLUTION: The trapezoid shown is divided into four triangles by its diagonals. The area of two triangles are indicated(9 and 25). What is the area of the whole trapezoid? <pre> Note: Ima      Log On


   



Question 1195835: The trapezoid shown is divided into four triangles by its diagonals. The area of two triangles are indicated(9 and 25). What is the area of the whole trapezoid?

Note: Image may not be proportional

Found 2 solutions by lotusjayden, ikleyn:
Answer by lotusjayden(18) About Me  (Show Source):
Answer by ikleyn(52835) About Me  (Show Source):
You can put this solution on YOUR website!
.
Let "a" be the shorter base of the trapezoid;

let "b" be the longer base of the trapezoid.


The triangles of the areas 9 and 25 square units are similar, 
with the similarity coefficient of 3%2F5 (smaller to larger).


Let h be the height of the smaller triangle drawn to its base "a";

Let H be the height of the larger triangle drawn to its base "b".


Then from the similarity of triangles,  b = %285%2F3%29a;  H = %285%2F3%29h.


We have then  %28a%2Bb%29%2F2 = %28a+%2B+%285%2F3%29a%29%2F2 = %288%2F6%29a = %284%2F3%29a;

              h + H = h+%2B+%285%2F3%29h = %288%2F3%29h.


The area of the trapezoid is  

    Area = %28%28a%2Bb%29%2F2%29%2A%28h%2BH%29 = %284%2F3%29a%2A%288%2F3%29h = %2832%2F9%29%2Aah;

    but  %28ah%29%2F2%29 = the area of the upper triangle = 9;  hence  ah = 2*9;  therefore

    Area = %2832%2F9%29%2A%282%2A9%29 = 32*2 = 64 square units.


ANSWER.  The area of the trapezoid is 64 square units.

Solved.