If bj > 0 for every j and if p ∞j =1 bj converges then prove that p ∞j=1( bj)2 converges. prove that the assertion is false if the positivity hypothesis is omitted. how about third powers?

I'm thinking it's 2 you are asked to explain the earth's magnetic field. which is the best reply? 1. the earth's magnetic south is similar to the north pole of a magnet. 2. the earth's core has a strong magnetic charge similar to the south pole of a magnet. 3. the earth's geomagnetic south is similar to the south pole of a magnet. 4. the earth's magnetic charge is not centered at either pole; it varies based on location.