Problem: The area of a circle is doubled when its radius r is increased by n. Then r equals:
Answer Choices:
A. n(2​+1)
B. n(2​−1)
C. n
D. n(2−2​)
E. 2​+1nπ​
Solution:
A=Ï€r2
2A=Ï€(r+n)2
2Ï€r2=Ï€(r2+2rn+n2)
r=n(1+2​); the value 1−2​ is not used