Sum of members

What is the sum of the first two members of the aritmetic progression if d = -4.3 and a3 = 7.5?

Result

s =  27.9

Solution:

d=4.3 a3=7.5 a2=a3d=7.5(4.3)=595=11.8 a1=a2d=11.8(4.3)=16110=16.1 s=a1+a2=16.1+11.8=27910=27.9d=-4.3 \ \\ a_{3}=7.5 \ \\ a_{2}=a_{3}-d=7.5-(-4.3)=\dfrac{ 59 }{ 5 }=11.8 \ \\ a_{1}=a_{2} - d=11.8 - (-4.3)=\dfrac{ 161 }{ 10 }=16.1 \ \\ s=a_{1}+a_{2}=16.1+11.8=\dfrac{ 279 }{ 10 }=27.9



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