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Let akand bkbe convergent sequences with ak→Land bk→Mas k→∞and let cbe a constant. Prove the indicated basic limit rules from Theorem 7.11. You may wish to model your proofs on the proofs of the analogous statements from Section 1.5.

Prove that akbk→LM.

Short Answer

Expert verified

Hence, the theorem is proved.

Step by step solution

01

Step 1. Given Information.

The objective is to prove thatakbk→LM.

02

Step 2. Forming the equations.

We use the definition of convergence for the sequence akand bk.

The sequence akconverges to L.

For given ε>0, there exists a positive integer such that

ak-L<ε2mfor k≥N..........(1)

The sequence bkconverges to M.

For given ε>0, there exists a positive integer Psuch that

bk-M<ε2L+1for k≥P...........(2)

There exists a positive integer msuch that

bk≤mfor allk...........(3)

03

Step 3. Proving the theorem.

Choose a positive integer Rsuch that R=maxN,P

akbk-LM=ak-Lbk+bk-ML≤ak-Lbk+bk-ML<ε2m×m+ε2L+1×Lfork≥R<ε2+ε2=ε

Thus, for k≥R,akbk-(LM)<εand hence, akbkis convergent.

Therefore, the value islimk→∞akbk=LM.

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