Question

ajutoor!!
repede va rooog​

Answer 1

Răspuns:

a37=a1+36r=473

a50=a1+49r=642

scădem orima din a doua ecuație

7r=169

r=169/7

a1=473-36*169/7=(473*7-6084)/7=

(3311-6084)/7=-2773/7

a1 primul termen

r rația

Explicație pas cu pas:

Answer 2

$\it a_{50}=a_{37}+13r \Rightarrow 642=473+13r\bigg|_{-473} \Rightarrow 13r=169 \bigg|_{:13}\Rightarrow r=13\\ \\ \\ a_1=a_{37}-36r=473-36\cdot13=473-468=5\\ \\ a_{30}=a_{37}-7r=473-7\cdot13=473-91=382\\ \\ \\ S_{30}=\dfrac{(a_1+a_{30})\cdot30}{2}=\dfrac{(5+382)\cdot30}{2}=387\cdot15=$