1)Find the third side of a triangle when two sides of the triangle is 4 and the included angle measuring 89 degrees 2)you were asked by your teacher to add up the numbers 1 to 100. Please show all work

3)determine if the foci for the following ellipse are correct and explain your reasoning 7x2 + 8y2 = 30; foci: (sqrt11, 0), (-sqrt11, 0)

1) The length of the third side is 5.607 units

2) The sum of the numbers from 1 to 100 is 5050

3) For the x-axis, foci: ((√15/28), 0) and (-(√15/28), 0)

For the y-axis, foci: (0, (√15/28)) and (0, -(√15/28))

Step-by-step explanation:

1) When two sides of the triangle are equal to 4 then the triangle is an isosceles triangle

Given that the included angle (the angle between the two sides) is 89°, we have;

The other two base angles are equal to {180 - 89)/2 = 91/2 = 45.5°

Therefore, we have from cosine rule;

a² = b² + c² - 2·b·c·cos(A)

We note that the angle opposite the third side is the included angle 89°, therefore, when we put a as the third side in the above equation, we have;

a² = 4² + 4² - 2×4×4×cos(89°)

a² = 31.44

a = 5.607

The length of the third side is 5.607 units

2) The numbers 1 to 100 form an arithmetic series with the first term, a = 1 and the common difference, d = 1 with the number of terms n = 100

The sum of an arithmetic progression, Sₙ, is given as follows;

Therefore, by plugging in the values, we have;

Sₙ = 100/2*(2*1 + (100 - 1)*1) = 100/2*(101) = 5050

The sum of the numbers from 1 to 100 is 5050

3) The foci of an ellipse 7·x² + 8·y² = 30 is found as follows;

Dividing both sides of the equation by 30 gives;

7/30·x² + 8/30·y² = 30/30

7/30·x² + 8/30·y² = 30/30

7/30·x² + 4/15·y² = 1

Which is of the form;

x²/a² + y²/b² = 1

For the x-axis we have

c² = a² - b²

c² = 30/7 - 15/4 = 15/28

h = 0, k = 0

Foci: ((√15/28), 0) and (-(√15/28), 0)

For the y-axis, we have;

x²/b² + y²/a² = 1

The foci are then (0, (√15/28)) and (0, -(√15/28)).

step-by-step explanation:

30% of $420 is 0.30($420) = $126 and $420 + $126 = $546.

or, 130% of $420 is 1.3($420) = $546.

notice that this is not the $600 original list price with which we started.

why doesn't this work?

the method does not work because 30% of $420 is not the same amount as the 30% of $600. it may seem obvious when stated this way, but it is a very common error made on problems of this type. we cannot just use the same percent and get back to the original amount because we are taking that percent of a different value.

to work problems of this type correctly, it is generally best to write an equation for the situation and then solve.

example: since (100% – 30%)(original price) = (sale price)

70% of the   (original price) is $420.

0.7x   = 420

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x = 600

the original cost was $600.

we may also solve this problem using the two-step method. working the problem in two steps requires us to use more algebra skills. we have to know that x = 1x (identity property of multiplicationtext annotation indicator) and that 1x – 0.3x = 0.7x (subtracting like terms). then we solve the problem as follows:

(original price) – 30%(original price) = sale price

x – 0.3x = 420

0.7x = $420

equation image indicator

x = 600

the original cost was $600.  

note that with both of the above methods we do obtain the correct original amount.

example: after a 5% pay raise, hermione is earning $22,680 per year. what was she earning before the pay raise?

105% of (original salary) = current salary

1.05x = 22,680

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x = 21,600

hermione earned $21,600 per year before the pay raise.

this is an example so maybe you will get how to at least do it!

f(x) = - 2/3x + 5; f(5/2)

substitute 5/2 in for x:

f(5/2) = -2/3(5/2) + 5

simplify the right side:

f(5/2) = -5/3 + 5

f(5/2) = 10/3

answer:

f(5/2) = 10/3

i hope this you!