Aregular decagon is mapped onto itsslf everytime it is rotated by how many degrees

36° is correct.

Step-by-step explanation:

The degree of rotational symmetry is equal to 360° divided by the number of sides of a regular polygon

360° ÷ 10 = 36°

A regular decagon is mapped onto itself every time it is rotated by 36°

Step-by-step explanation:

A regular decagon means a polygon with 10 sides and all sides are equal.

Refer the given figure, if we rotate by 36° we will get same decagon.

So a regular decagon is mapped onto itself every time it is rotated by 36°

the value of v.w= -12.

step-by-step explanation:

we are given three vector r,v and w as:

r = < 5, -5, -2> ; v = < 2, -8, -8> ; w = < -2, 6, -5>

we know that r,v and w could also be represented as:

r=5i-5j-2k

v=2i-8j-8k

and w= -2i+6j-5k

where i,j and k are the unit vectors of x,y and z-axis respectively.

also we know that it has the following property:

i.i=1 ; j.j=1; k.k=1

and i.=j.i=i.k=k.i=j.k=k.j=0

i.e. when we multiply two vectors or we find it's dot product we need to only multiply the components of x coordinates with each other; y with each other and z with each other.

hence, v.w= (2i-8j- -2i+6j-5k)

                  = 2×(-2)+(-8)×(6)+(-8)×(-5)

                  = -4-48+40

                  = -12

hence, v.w= -12