Question

n the diagram below, points $A,$ $E,$ and $F$ lie on the same line. If $ABCDE$ is a regular pentagon, and $\angle EFD=90^\circ$, then how many degrees are in the measure of $\angle FDE$?
[asy]
size(5.5cm);
pair cis(real magni, real argu) { return (magni*cos(argu*pi/180),magni*sin(argu*pi/180)); }

pair a=cis(1,144); pair b=cis(1,72); pair c=cis(1,0); pair d=cis(1,288); pair e=cis(1,216);
pair f=e-(0,2*sin(pi/5)*sin(pi/10));
dot(a); dot(b); dot(c); dot(d); dot(e); dot(f);
label("$A$",a,WNW);
label("$B$",b,ENE);
label("$C$",c,E);
label("$D$",d,ESE);
label("$E$",e,W);
label("$F$",f,WSW);
draw(d--f--a--b--c--d--e);
draw(f+(0,0.1)--f+(0.1,0.1)--f+(0.1,0));
[/asy]

Answer 1

Answer:

18

Step-by-step explanation:

Each interior angle of a regular pentagon is 108 degrees. So Angle AED is 108 degrees. Since Angle AEF is a straight line (180 degrees), Angle FED is 72. This is because 180-108 = 72. Now, since a triangle has a total of 180 degrees, we add 72 and 90, because those are the 2 degrees we have calculated. This gives us a total of 162. Now, we subtract 162 from 180 to find out the degree of Angle FDE. This is 18. So our final answer is 18.

Sidenote: I hope this answer helps!

Answer 2

The properties of a pentagon and the given right triangle formed by

segments EF and FD give the measure of ∠FDE.

Response:

• ∠FDE = 18°

Which properties of a pentagon can be used to find ∠FDE?

The given parameters are;

A, E, F are points on the same line.

ABCDE is a regular pentagon

∠EFD = 90°

Required:

The measure of ∠FDE

Solution:

The points A and E are adjacent points in the pentagon, ABCDE

Therefore;

line AEF is an extension of line side AE to F

Which gives;

• ∠DEF is an exterior angle of the regular pentagon = $\frac{360 ^{\circ}}{5}$ = 72°

∠EFD = 90°, therefore, ΔEFD is a right triangle, from which we have;

The sum of the acute angles of a right triangle = 90°

Therefore;

∠DEF + ∠FDE = 90°

Which gives;

72° + ∠FDE = 90°

∠FDE = 90° - 72° = 18°

• ∠FDE = 18°

Learn more about the properties of a pentagon here:

https://brainly.com/question/15392368