# Help with a geometry word problem! Triangle Side lengths! Suppose a chair has a seat that's an isosceles triangle and the congruent sides measure 1.5 ft. A second chair has a triangular seat w/a...

Help with a geometry word problem! Triangle Side lengths!

Suppose a chair has a seat that's an isosceles triangle and the congruent sides measure 1.5 ft. A second chair has a triangular seat w/a perimeter of 5 1/10 ft, and it's congruent to the first seat. What is a side length of the second seat?

pohnpei397 | Certified Educator

If you have stated the question properly, then all you have to remember is that congruent triangles have both sides and angles that are congruent.  This is as opposed to similar triangles that have congruent angles, but not necessarily sides.

If these two triangles are congruent, they both have the same side lengths and the same total perimeter.   Given that, we can see that the sides of the second triangle (and the first) are 1.5 feet, 1.5 feet and 2.1 feet.

The reason for this is that the perimeter of a triangle is the sum of all its sides.  We know that two of the sides are 1.5 feet each.  Those two sides, then, come out to 3.0 feet in length.  If the perimeter of the whole triangle is 5.1 feet, then the remaining side must be 2.1 feet.

hala718 | Certified Educator

Given:

Chair 1:  isoscale traingle with sides:

1.5 , 1.5   and x.

Chair 2: congruent to chair 1:

Then, sides for chair1 = sides for chair 2.

also , Perimeter for chair1 = perimeter for chair 2.

Given perimeter for chair 2= 5 1/10 = 5.1

Then:

perimeter of chair1 = perimeter of chair 2= 1.5+ 1.5 + x = 5.1

==> 3 + x = 5 1/10

==> x= 2 1/10= 2.1

Then the third side of the triangles = 2

neela | Student

The seat of the first chair  is an isosceles  triangle with its equal sides measuring 1.5 feet.

The  sides  of the seat of the second chair are congruent  with the sides of the first chair. Therefore  the seat of the second chair is also isosceles. So the seat of the second chair has  two sides each measuring 1.5 feet. As per the given information  the seat of the second chair has a perimeter 5 1/10 ft. Thus the second chair has the another side which should measure 5 1/10 ft - 2*1.5ft = (5.1 - 3) ft = 2.1 ft.

So the measurents of the sides of the second chair  are: 1.5 feet, 1.5 feet and the other side 2.1 feet.