Q. Find the perimeter of the isosceles triangle whose un

Great question. It tests a few key concepts simultaneously.

1. Properties of isosceles triangles: among others, if the median is drawn to the base (BM in diagram below):

a) the median is the altitude, which we need because we are given area and need to find perimeter, which will rely on property (1-c) below
b) the median/altitude is the perpendicular bisector of the base
c) it produces two congruent right triangles

Diagram is below

2. Draw a triangle ABC with base 16, other two equal sides labeled X. AB=BC

3. Draw the median, BM. Its height is derived from given area. Triangle area = 1/2*b*(height) => 48 = (1/2)(16)(BM) => 96 = 16 * BM => Height/BM = 6

4. Base AC is bisected perpendicularly, so we have two triangles with 90-degree angles and congruent sides, per c above. \(\frac{AC}{2}\) = \(\frac{16}{2}\)=8, 8=AM=CM. We now have two right triangles with values for legs: BM is 6, AM is 8 (CM also = 8).

5. Properties of right triangles: if you have two legs in the ratio 3x:4x, the hypotenuse will be 5x. (3-4-5 right triangle.) And per (a) and (c) above=>

6. Each equal side of the isosceles triangles is the hypotenuse of a 3-4-5 right triangle. You can either do the math with Pythagorean theorem or remember that 3-4-5 has all kinds of variations, including 6-8-10. We have BM is 6, AM is 8. So hypotenuse is 10.

Now you have two hypotenuse/equal sides of isosceles triangle with value X = 10. Find perimeter. 10 + 10 + 16 = 36.

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