Which of the following is equivalent to....

Question

anonymous · Answer

$$\sum_{n=4}^{7} -2n+3$$

anonymous · Answer

its n=4 on the bottom

anonymous · Answer

to do this, just plug in the values of n from 4 to 7, each time increase the value of n by 1. Then sum all of them

so you should get:
(-8+3)+(-10+3)+(-12+3)+(-14+3) = -44+12 = -32

anonymous · Answer

can you also help me with this one? Given the sequence 9, 15, 21, which of the following is equivalent to $$\sum_{n=5}^{8}a _{n}$$

anonymous · Answer

you see, the difference is 6, 9 to 15, and 15 to 21.
so the formula must be 6n + something
you will find that "something" to be -21, so that the answers match

therefore, the sigma notation becomes:
$$\sum_{n=5}^{8}6n-21$$

anonymous · Answer

168
		102
		144
		54

anonymous · Answer

those are my choices

anonymous · Answer

well, I have no idea what your question is asking you then... I'm sorry.

anonymous · Answer

like the 1st one just solve the second equation is knew it changed to 21 but idk what to do after that?

anonymous · Answer

oh, just solve it? then just sum up 9+15+21+27 = 72 :)
but 72 is not available in the choices...

anonymous · Answer

kk