Question

Find the sum of the first 90 terms of the sequence –4, –1, 2, 5, 8, ...

Answer 1

Hello : 
-1-(-4) =2-(-1)=5-2=8-5=3     ( arhtmitic sequence   r= 3)
Un = U1+(n-1)r
U90 = -4+(90-1)(3)= 263
sum = n/2 (U1 +U90)
sum = 90/2(-4+263) = 11655

Answer 2

Answer:

11655 is correct

Step-by-step explanation: