Bunuel
If each of the three triangles has an area of 18, what is the perimeter of the figure they form?
A) 54
B) 36 + 18√2
C) 48 + 18√2
D) 54√2
E) 54 + 27√2
Attachment:
perimeter.png [ 33.42 KiB | Viewed 1725 times ]
Parallel and perpendicular lines indicate right angles
Find other angle measures; these figures are probably special triangles
Perimeter: Find side length from area, hypotenuse length from special properties
•
90° angles at A and E (two angles at E)Line 1 || Line 2
Line 1 ⍊ Line 3, thus
Line 2 ⍊ Line 3
a line perpendicular to one of two parallel lines
is perpendicular to the other line also
•
∠ D = 45 = ∠ B(alternate interior angles of parallel lines 1 and 2 cut by transversal)
•
∠ B = 45° = ∠ F (alternate interior angles of parallel lines 4 and 5 cut by transversal)
•
∠ G = ∠ C (two angles at C) = 45°Each triangle so far has one 90° and one 45° angle. The other is 45°
(90 + 45) = 135° and then (180°-135°) =
45°The three triangles are right isosceles triangles
Sides opposite equal angles are equal.
•
Perimeter? Need side lengths. Derive them from areaArea of right isosceles triangle,
\(A=\frac{s^2}{2}\)Same as
\(\frac{b*h}{2}\); here \(b = h\)\(\frac{s^2}{2} = 18\)
\(s^2 = 36\)
\(s = 6\)Hypotenuse?*
Isosceles right triangles have sides in ratio
\(x: x: x\sqrt{2}\)(\(x\) and \(x\) are opposite 45° angles, \(x\sqrt{2}\) is opposite 90° angle)
\(s = 6\) corresponds with \(x\)
Hypotenuse corresponds with \(x\sqrt{2} = 6\sqrt{2}\)
Perimeter:Legs:
\(6 * 6 = 36\)Hypotenuses:
\(3 * 6\sqrt{2} = 18\sqrt{2}\)\(P = 36 + 18\sqrt{2}\)Answer B
*Or use Pythagorean theorem: \(Side^2+Side^2=Hypotenuse^2\)
\(8^2+8^2=H^2\)
\(H^2=(64+64)=128\)
\(\sqrt{H^2}=\sqrt{128}\)
\(\sqrt{H^2}=\sqrt{64*2}=(\sqrt{64}*\sqrt{2})\)
\(H=8\sqrt{2}\)