what is the common difference of an A.P in which a21 - a7 = 84 ?
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Answer: The common difference of an A.P in which a21 - a7 = 84 is 6
Step-by-step explanation:
Consider f is the first term and d is the common difference of an AP
We know an=f+(n-1)d
f21=a+(21−1)d=f+20d equation1
f7=a+(7−1)d=f+6d equation2
f21−f7=84
Substracting equation 2 from equation 1
f+20d−f−6d=84
14d=84
d=84/14
d=6
Thus the common difference is 6.
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