Answers

The Brainliest Answer!
2015-03-15T10:17:20+05:30

This Is a Certified Answer

×
Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
First term(f)=7
last term(l)=49
common difference=d
n(number of terms)=n
sn(sum)=420
sn=

 \frac{n}{2} (f+l) \\ 
 \\ 420= \frac{n}{2}(7+49) \\  \\ 
840=n*56 \\ 
56n=840  \\ 
n= \frac{840}{56}=15
number of terms=15

n=

 \frac{l-f}{d}+1 \\  \\ 
15= \frac{49-7}{d}+1 \\  \\ 
15= \frac{42}{d} +1 \\  \\ 
14= \frac{42}{d}    \\  \\ 
14d=42 \\ 
d= \frac{42}{14}=3

common difference=3
6 4 6
2015-03-15T10:42:49+05:30

This Is a Certified Answer

×
Certified answers contain reliable, trustworthy information vouched for by a hand-picked team of experts. Brainly has millions of high quality answers, all of them carefully moderated by our most trusted community members, but certified answers are the finest of the finest.
a=7,\ a_n=49,\ S_n=420\\let\ the\ common\ difference=d\\ \\S_n= \frac{n}{2}[a+a_n] \\ \\ \Rightarrow 420=\frac{n}{2}[7+49]\\ \\ \Rightarrow 420=\frac{n}{2}[56]=28n\\ \\ \Rightarrow n= \frac{420}{28} =15\\ \\we\ know\ that\ a_n=a+(n-1)d\\ \\ \Rightarrow 49=7+(15-1)d \\ \\ \Rightarrow 49-7=14d\\ \\ \Rightarrow 14d=42\\ \\ \Rightarrow d= \frac{42}{14}=3 \\ \\ Common\ difference\ is\ 3.
5 3 5