The greek mathematician eratosthenes (ca. 276-195 bc) measured the circumference of the earthfrom the following observations. he noticed that on a certain day the sun shone directly down a deep wellin syene (modern aswan). at the same time in alexandrea, 500 miles north (on the same meridian), therays of the sun shone at an angle of 7.2° to the zenith. use this information to find theradius and circumference of the earth.

Radius of the Earth is 3978.8 Miles

Circumference of the Earth is 25000 Miles

Step-by-step explanation:

The angle of the sun shone at an angle of 7.2° to the zenith

This means that the angle of the sector of the circle is 7.2° (θ)

S = Length of the sector of the circle = 500 miles

r = radius of earth

Converting 7.2° to radians

∴ Radius of the Earth is 3978.8 Miles

∴ Circumference of the Earth is 25000 Miles

it's d

step-by-step explanation:

see explanation

step-by-step explanation:

a

(6r + 7) + (13 + 7r) ( remove brackets and collect like terms )

= 6r + 7 + 13 + 7r

= 13r + 20

b

remove brackets and collect like terms

13 - r - 1 + r

= 12 - r

c

remove brackets and collect like terms

= - 8 - r + 2r - 4

= - 12 + r

d

remove brackets and collect like terms

= 7r - - - 6r

[-   - = - - = - ]

= r -