Answer: 119,616
You may have to erase the comma when inputting the answer.
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Explanation:
The author sells 21,000 books in the first month.
Then they sell 21,000*(1-0.12) = 21,000*(0.88) = 18,480 in the second month.
Then they sell 18,480*(1-0.12) = 18,480*(0.88) = 16,262.4 = 16,262 in the third month.
And so on. These values follow a geometric sequence with first term a = 21,000 and common ratio r = 0.88
We can think of the 0.88 as 88% of the original value (since losing 12%, we keep the remaining 88%)
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Use the formula below to sum the first 9 terms of the geometric sequence
Plug in a = 21000 and r = 0.88

The author sold about 119,616 books over the course of the first nine months.
Answer:
complementary
Step-by-step explanation:
because the angles add up to 90°
To find W⊥, you can use the Gram-Schmidt process using the usual inner-product and the given 5 independent set of vectors.
<span>Define projection of v on u as </span>
<span>p(u,v)=u*(u.v)/(u.u) </span>
<span>we need to proceed and determine u1...u5 as: </span>
<span>u1=w1 </span>
<span>u2=w2-p(u1,w2) </span>
<span>u3=w3-p(u1,w3)-p(u2,w3) </span>
<span>u4=w4-p(u1,w4)-p(u2,w4)-p(u3,w4) </span>
<span>u5=w5-p(u4,w5)-p(u2,w5)-p(u3,w5)-p(u4,w5) </span>
<span>so that u1...u5 will be the new basis of an orthogonal set of inner space. </span>
<span>However, the given set of vectors is not independent, since </span>
<span>w1+w2=w3, </span>
<span>therefore an orthogonal basis cannot be found. </span>