Question

s8=120 a7:a2 = 5 найти а1 и а2

Answer 1

$S _{8}= 120\ frac{ a_{7} }{ a_{2} }=5\\ frac{ a_{1} +6d}{ a_{1}+d } =5\\5 a_{1}+5d= a_{1}+6d\\d=4 a_{1} \\S _{8} = frac{2 a_{1} +7d}{2}*8=(2 a_{1}+28 a_{1})*4\\30 a_{1}*4=120\\30 a_{1}=30\\ a_{1}=1\\ a_{2}= a_{1}*d= a_{1}+4 a_{1}=5 a_{1} =5*1=5$