Question

wyznacz ciąg arytmetyczny mając dane a5+a7 =20 ia4+a11 = 26

Answer 1

a5+a7 =20

a4+a11 = 26

 

a1 + 4r + a1 + 6r = 20

a1 + 3r + a1 + 10r = 26

 

2a1 + 10r = 20     /*(-1)

2a1 + 13r = 26

 

-2a1 - 10r = -20

2a1 + 13r = 26

---------------------

            3r = 6

              r = 2

 

2a1 + 10r = 20

2a1 + 10 * 2 = 20

2a1 = 20 - 20

2a1 = 0

a1 = 0

 

odp. Jest to ciąg: 0, 2, 4, 6, 8, 10, 12,........