What is the formula for the circumference of a circle in terms of r

C = 2πr

Step-by-step explanation:

The formula for the circumference of a circle is C = πd, and since the diameter, d, is equal to double the radius, 2r, we can replace 2r for d. Giving us C = 2πr

42.4

step-by-step explanation:

convert to decimal

we have three similar triangles, because each has a right angle and shares an angle.   let's write the angles in order: opposite to short leg, long leg, hypotenuse.

cab similar to bad similar to cbd

or as ratios,

ca: ab: cb = ba: ad: bd = cb: bd: cd

we also know

ac = ad + cd

(ad+cd): ab: cb = ba: ad: bd = cb: bd: cd

(ad+cd)/cb=cb/cd

we have cb=6, ad=5 and seek x=cd.

we reject the negative root and conclude x=4

answer: 4