Will fan and medal whoever helps me .

A sequence starts at 500 and 80 is subtracted each time .
500 , 420 , 340 ...
The sequence continues in the same way . Write the FIRST TWO NUMBERS in the sequence which are less than zero .
Thank you :)

Question

Will fan and medal whoever helps  me . 

A sequence starts at 500 and 80 is subtracted each time . 
500 , 420 , 340 ... 
The sequence continues in the same way . Write the FIRST TWO NUMBERS in the sequence which are less than zero . 
Thank you :)

shiraz14 · Answer

This is an A.P. with T1=500 & d=-80. For an A.P., Tn=T1+(n-1)d. So we have:

Tn = 500 + (n-1)(-80) < 0
80n > 580
--> n>7.25
n=8 
 When n=8, 
T8 = 500 + 7(-80) = 500 - 560 = -60 (Answer)
The next term, T9 = -60 - 80 = -140 (Answer)