Question

Найти a1 и d если
a1+a5=7; a15=32

Answer 1

$left { {{a _{15} =32} atop {a _{1} +a _{5}=7 }} right.$

$left { {{a _{1}+14d=32 } atop {a _{1}+a _{1} +4d=7 }} right.$

$left { {{a _{1} +14d=32} atop {2a _{1}+4d=7 }} right.$

$-left { {{a _{1}+14d=32 } atop {a _{1} +2d=3,5}} right.$
___________
  12d = 28,5
     d = 2,375
$a _{1}= 32 - 14*2,375=32-33,25=-1,25$