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Sum of first n terms of an arithmetic sequence is 5n² + 2n. What is the 21st term of the sequence ?

A102

B107

C202

D207

Answer:

D. 207

Read Explanation:

Pn2+qnPn^2+qn

p=d2p=\frac{d}{2}

p+q=fp+q=f

d=5×2=10d=5\times 2 = 10

5+2=f5+2=f

x21=f+20d=7+20×10=207x_{21}=f+20d=7+20\times10=207


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