Arithmetic progression

In some arithmetic progression applies:

5a2 + 7a5 = 90
s3 = 12

Find the first member a =? and difference d =.

Correct answer:

a =  2
d =  2

Step-by-step explanation:


5·(a+d)+7·(a+4·d) = 90
a+(a+d)+(a+2·d) = 12

12a+33d = 90
3a+3d = 12

Row 2 - 3/12 · Row 1 → Row 2
12a+33d = 90
-5.25d = -10.5


d = -10.5/-5.25 = 2
a = 90-33d/12 = 90-33 · 2/12 = 2

a = 2
d = 2

Our linear equations calculator calculates it.



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