Difference 5222

Determine the difference and the first term of AP if a3 + a4 = 48, a7 = 80.

Correct answer:

a =  -16
d =  16

Step-by-step explanation:


(a+2d)+(a+3d)=48
a + 6d = 80

(a+2·d)+(a+3·d)=48
a + 6·d = 80

2a+5d = 48
a+6d = 80

Row 2 - 1/2 · Row 1 → Row 2
2a+5d = 48
3.5d = 56


d = 56/3.5 = 16
a = 48-5d/2 = 48-5 · 16/2 = -16

a = -16
d = 16

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