Question

Escreva uma PA onde : o terceiro termo vale 13 e o sétimo termo vale 25.

Answer 1

$[\\a_3=13\\a_7=25\\\\13=a_1+(13-1)r\\13=a_1+12r(I)\\\\25=a_1+(7-1).r\\25=a_1+6r(II)\\\\(II)*-2 =-50=-2a1-12r\\(I)+(II)=-37=-a_1\\a_1=37\\\\25=37+(7-1).r\\-12=6r\\\\r=-\frac{12}{6}\\\\r=-2\\\\a_n=37+(n-1).-2$