Question

Se consideră progresia aritmetică in care a1=7 si a2=37.calculati suma primilor 10 termeni ai progresiei

Answer 1

$a_1=7\\a_2 = 37 \\ \\\\ r = a_2 - a_1 = 37-7 = 30 \\\\ a_{10} = a_1+(10-1)r = 7+9\cdot 30 = 7+270 = 277 \\ \\\\ S_{10} = \dfrac{(a_1+a_{10})\cdot 10}{2} = (7+277)\cdot 5} = 284\cdot 5 = \boxed{1420}$