d= the common difference
t1= the first term
we have the following:
n=25
d=3
t1=-2
tn=?
Substituting the information, we should have:
S25=(25/2)(2(-2)+3(25-1))
S25=(12.5)(-4+3(24))
S25=(12.5)(-4+72)
S25=(12.5)(68)
S25= 850
Thus, the sum of the first 25 terms of (-2, 1, 4, 7...) is 850.
Shields are down to 70%!! Arm torpedoes and fire multiple-phasers!!
Now, to solve for tn using the information we have,
tn=t1+(n-1)d
tn= -2+3(25-1)
tn= -2+3(24)
tn= -2+72
tn= 70
Their torpedoes are ripping right through our shields!!! I think we should learn more about them...
Finding the SUM of all multiples of 7 between 232 and 677.
t1= 238
tn= 672
d= 7
n= ?
First, we must find the value of n
tn=t1+(n-1)d
672= 238+7(n-1)
434= 7n-7
441=7n
63=n
The environmental controls and life support are failing. Shields are down to 0%.. We've lost 9 decks, main computer is down, multiple breaches across the ship, phasers and torpedo launchers are down... What are we going to do? Continue to learn...
S63= (63/2)(2(238)+7(63-1))
S63= (31.5)(476+7(62))
S63= (31.5)(476+434)
S63= (31.5)(910)
S63= 28665
Computer.... Initiate Self-Destruct Sequence....
Please the following sites if you are still having problem with this topic: Arithmetic Sequence and Sequences.
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