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3 years ago

Someone please help! I have spent lots of time on this and I’m still confused

Mathematics

1 answer:

vfiekz [6]3 years ago

3 0

Answer:

its the 3rd choice.

Step-by-step explanation:

Firstly, we find angle BDC (180-90-30=60)

Now that we found it we can use the sine rule to find DB (which i put as an x), which is sin60/14=sin30/x, by cross multiplication, we find that its equal to a decimal number, i will use its root version to this easier, its equal to 14sqrt3/3 inches.

And now we use the pythagorean theorem to find DC, we find that it is equal to 28sqrt3/3

Now, we find angle BAC (180-90-(30+15)=45)

Again, we use the sine rule to find AB (whom i will refer to as x and from whom we will subtract DB to find the length of AD), so we cross multiply in sin45/14=sin(30+15)/x, it is equal to 14.

So since AB-DC=AD

14-(14sqrt3/3)= 5.917096231 (and we ound that to a 5.9)

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Savatey [412]

we have that

$300 + 150 + 75 +...$

Let

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we know that

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Is a geometric sequence

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$a(4)=75*0.50$

$a(4)=37.5$

Find the value of $a5$

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$a(5)=37.5*0.50$

$a(5)=18.75$

Find $S5$

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Alternative Method

Applying the formula

$S_n=\frac{a_1 (1-r^n)}{1-r} \\\\a_1=300 \\ r=\frac{1}{2}\\\\ S_5=\frac{300(1-(\frac{1}{2})^5)}{1-\frac{1}{2}}\\\\=\frac{300(1-\frac{1}{32})}{\frac{1}{2}}\\\\=\frac{300 \times \frac{31}{32}}{\frac{1}{2}}\\\\=\frac{75 \times \frac{31}{8}}{\frac{1}{2}}\\\\=\frac{\frac{2325}{8}}{\frac{1}{2}}\\\\=\frac{2325}{8} \times 2\\\\=\frac{2325}{4}\\\\=581 \frac{1}{4}\\\\=581.25$

therefore

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$581.25$

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