Question

Como escrevo PA em que a2+a6 = 20 e a4+a9 = 35 ??????????????????????????

Answer 1

$\left \{ {{a_1+(2-1)r+a_1+(6-1)r=20} \atop {a_1+(4-1)r+a_1+(9-1)r=35}} \right. \\ \\ \left \{ {{a_1+r+a_1+5r=20} \atop {a_1+3r+a_1+8r=35}} \right.\\ \\ \left \{ {{2a_1+6r=20} \atop {2a_1+11r=35}} \right.\\ \\ 2a_1 = 20-6r\\ substitui\, na\, equacao\,2\\ 2a_1+11r=35\\ 20-6r+11r=35\\ 5r=15\\ r= \frac{15}{5} = 3 \\ 2a_1=20-6.3=.20-18=2 \\ 2a_1=2=\ \textgreater \ a_1= 1$