PLEASE HELP ME on #57 WITH ALL WORK SHOWN!!

Tmr is my exam pls help...

Explanation:

Recall that quadratic form is ax^2+bx+c.

So we need an x^2 term followed by an x term, then a constant at the end.

It may not look it, but the given equation is nearly in quadratic form.

Rewrite 9^(2x) as (9^x)^2

We get this equivalent equation (9^x)^2 - 2*(9^x) - 3 = 0

From here, let's make w = 9^x. Replace every copy of '9^x' with 'w' and we end up with this new simpler equation: w^2 - 2w - 3 = 0

From here we can use the quadratic formula or factor. I'll factor.

w^2 - 2w - 3 = 0

(w - 3)(w + 1) = 0

w-3 = 0 or w+1 = 0

w = 3 or w = -1

Now we use these values of w to find x

If w = 3, then,

w = 9^x

3 = 9^x

log(3) = log(9^x)

log(3) = x*log(9)

x = log(3)/log(9)

x = log(3)/log(3^2)

x = log(3)/(2*log(3))

x = 1/2

At the last step, we have the log(3) terms cancel.

Repeat for w = -1

w = 9^x

-1 = 9^x

log(-1) = log(9^x)

We run into a problem. The log of any negative number is not a real number output. In other words, 9^x is never negative. Raising any positive number to a real number output leads the result to be positive. Take a look at the graph of y = 9^x to confirm this.

In short, w = -1 is extraneous so it doesn't lead to any x value solution.

So only w = 3 is useful.

Ultimately, the only solution is x = 1/2.

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

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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!