Question

The sum of the first 10 terms of the arithmetic series for which a1 =

is
180, a2 =
150, and a3 = 120

Answer 1

`450`

Explanation:

`a_1=180\\a_2=150\\a_3=120`

`d=-30`

`a_n=-30n+210`

`a_4=90\\a_5=60\\a_6=30\\a_7=0\\a_8=-30\\a_9=-60\\a_(10)=-90`

`180+150+120+90+60+30+0-30-60-90=450`