EIV Guide 3 Page 122

[nyc.willchan]

Directly from the book:

If x=5 to the 20th power and y=5 to the 19th power, what is x - y, in terms of y?

(C) 4y

Here, we must connect the given values of x and y in some way. Since 5 to the 20th power = 5 * 5 to the 19th power, we can write x=5y. Now the target expression x - y can be rewritten as 5y-y=4y.

I do not understand why how 5*5 to the 19th power is the same as x=5y.

[adiagr]

Directly from the book:

If x=5 to the 20th power and y=5 to the 19th power, what is x - y, in terms of y?

(C) 4y

Here, we must connect the given values of x and y in some way. Since 5 to the 20th power = 5 * 5 to the 19th power, we can write x=5y. Now the target expression x - y can be rewritten as 5y-y=4y.

I do not understand why how 5*5 to the 19th power is the same as x=5y.

the question says:

x - y = 5^20 - 5^19

Take (5^19) common, the expression becomes:


5^19. (5 - 1) = 5^19 . 4

Now y = 5^19 .

so expression becomes 4y

[nyc.willchan]

I am sorry but I still do not understand what I asked earlier based on the explanation below after your first sentence:

"Take (5^19) common, the expression becomes:


5^19. (5 - 1) = 5^19 . 4

Now y = 5^19 .

so expression becomes 4y"

There are symbols, words, etc which I am not familiar with. ie Common? ie 5^19 - yes. What does the period after the 19 represent (in both instances on the second quoted line)?

Thanks for your help

[adiagr]

I am sorry but I still do not understand what I asked earlier based on the explanation below after your first sentence:

"Take (5^19) common, the expression becomes:


5^19. (5 - 1) = 5^19 . 4

Now y = 5^19 .

so expression becomes 4y"

There are symbols, words, etc which I am not familiar with. ie Common? ie 5^19 - yes. What does the period after the 19 represent (in both instances on the second quoted line)?

Thanks for your help

Will try to help.

5^19 means 5 raised to the power 19.

x.y means => x multiplied by y.

See expression is:

5^20 - 5^19

This can be written as: 5 .(5^19) - 1. (5^19)

Taking (5^19) out, we can write

(5^19) (5-1)

which is (5^19)(4)

[nyc.willchan]

PERFECT! Now it makes sense. You factored both expressions out which in turn becomes y. That was the missing link. Again, thanks a lot for your help.

[tim]

thanks, adiagr..