Question

Progresie aritmetica
a1= 6 ,r = 8
da se determine: a2, a3,a10,s10​

Answer 1

formula pentru termenul general:

$a_n=a_1+(n-1)r$

$a_2=a_1+(2-1)r=6+8=14\\a_3=a_1+(3-1)r=6+2\cdot8=6+16=22\\a_{10}=a_1+(10-1)r=6+9\cdot8=6+72=78$

Formula generala pentru suma:

$S_n=n\cdot\dfrac{a_1+a_n}{2}$

$S_{10}=10\cdot\dfrac{a_1+a_{10}}{2}=10\cdot\dfrac{6+78}{2}=10\cdot\dfrac{84}{2}=10\cdot42=420$