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A equation for the ninth term of a arithmetic sequence who seventh term is 21 and common difference of 5

Sagot :

Answer:

[tex]9th=31[/tex]

Step-by-step explanation:

From the question we are told that:

Seventh term [tex]7th= 21[/tex]

Common difference [tex]d= 5[/tex]

Generally Equation for seventh term

[tex]7th=a+(7-1)d[/tex]

Therefore the  First Term is given as

[tex]a=7th-(7-1)d[/tex]

[tex]a=21-6*5\\a=-9[/tex]

Generally the equation for 9th term is mathematically given by

[tex]9th=a+8d[/tex]

[tex]9th=-9+8(5)[/tex]

[tex]9th=31[/tex]