18,-13,-8,- find the above sequential formula

The first term (a) is - 18

You add 5 to get to the next term. Or you can solve it by taking any 2 consecutive terms and find their difference.

Formula

d = t4- t3

Givens

t4 = - 3

t3 = - 8

Solution 1

d = t4 - t3             Substitute

d = -3 -  ( - 8)        Remove the brackets

d = -3 + 8             Combine  

d = 5                    Difference

Remark

Find the general formula

tn = - a + (n - 1)d      Substitute

So term 20 =           Example    

t20 = -18 + (20 - 1)*5 Combine the inside of the brackets. Remove the brackets

t20 = - 18 + 19*5          Combine 19 and 5          

t20 = -18 + 95              "Subtract"

t20 = 77                        Answer