Question

For an arithmetic sequence where a1 = 17 and the common difference is 5, find s7. A. 229 B. 235 C. 224 D. 219 please show steps 11 points

Answer 1

Answer: C. 224

Step-by-step explanation:

Given : The first term of an arithmetic sequence = $a_1=17$

Common difference : $d=5$

We know that the sum of first n terms is given by :-

$S_n=\dfrac{n}{2}(2a+(n-1)d)$

Now, for n=7 we have

$S_7=\dfrac{7}{2}(2(17)+(7-1)(5))\\\\\Rightarrow\ S_7=\dfrac{7}{2}(34+30)\\\\\Rightarrow\ S_7=\dfrac{7}{2}(64)\\\\\Rightarrow\ S_7=224$

Answer 2

Answer:

The correct answer is C. 224

Step-by-step explanation:

Sn = n/2 (2*A1 +d(x-1))

S7=7/2(2*17+5(7-1))

S7=7/2(34+30)

S7=7/2(64)

S7=7*64/2

S7=7*32/1

S7=224

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