Arithmetic 81798

Two arithmetic sequences have the same first term. The nth term of the first sequence is 15, and of the second sequence, 21. The sum of the first n terms of the first sequence is 63, and of the second sequence, 84. Write the sums of the first n terms of both sequences

Correct answer:

a1 =  3
b1 =  3

Step-by-step explanation:

a1=b1 a=15 b=21  s1=63 s2=84  s1 = (a1+a)/2 n s2 = (a1+b)/2 n  s1/s2 = (a1+a)/(a1+b)  s1 (a1+b)=(a1+a) s2 63 (a1+21)=(a1+15) 84  21a1=63  a1=2163=3  a1=3  s1 a1+s1 b=a1 s2+a s2  a1=s1s2a s2s1 b=638415 8463 21=3  n=2 s1/(a1+a)=2 63/(3+15)=7
b1=a1=3



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