Calculate "(2a+8b)(4a-2b)"

15 replies to this topic

#1 -Alex-

-Alex-

Noob Hunter

• 2,761 posts
• Joined: 08-August 06
• Location: Oslo, Norway

Posted 22 November 2012 - 08:24

Hi all,

I'm interested in becoming a pilot and was just reading some information online at a pilot programme. They give a sample entrance exam, and on it is this question (question 9):

Calculate:
(2a+8b)(4a-2b)

Is this supposed to read (2a+8b)+(4a-2b)=0, or am I missing something?

I'm not looking for the answer to this question, rather, how to calculate it; for my own knowledge.

Thanks!

#2 XerXis

XerXis

Neowinian Senior

• 5,137 posts
• Joined: 13-February 06
• Location: Belgium

Posted 22 November 2012 - 08:32

(2a+8b)(4a-2b)=8a^2 - 4ab + 32ab - 16b^2=8a^2 + 28ab - 16b^2

probably just to see if you know your distribution rule

cell tech

• 1,436 posts
• Joined: 04-November 07

Posted 22 November 2012 - 08:37

It would be read as "(2a+9b)*(4a-2b)" with no absolute answer: you would be solving for one variable in terms of the other: as in "a=something b" or "b=something a"

Edited by abecedarian paradoxious, 22 November 2012 - 08:42.

#4 Neo003

Neo003

Those who believe in telekinetics, raise my hand.

• 8,494 posts
• Joined: 12-June 03

Posted 22 November 2012 - 08:37

Hi all,

I'm interested in becoming a pilot and was just reading some information online at a pilot programme. They give a sample entrance exam, and on it is this question (question 9):

Is this supposed to read (2a+8b)+(4a-2b)=0, or am I missing something?

I'm not looking for the answer to this question, rather, how to calculate it; for my own knowledge.

Thanks!

Spoiler

#5 Xahid

Xahid

Anokha Neowinian

• 6,196 posts
• Joined: 04-November 01
• OS: Windows 7 Ultimate

Posted 22 November 2012 - 08:37

Is this supposed to read (2a+8b)+(4a-2b)=0, or am I missing something?

No, I believe it means (2a+8b)x(4a-2b)=0
Since brackets () mean multiplication so its not necessary to use 'x' specifically.

#6 OP -Alex-

-Alex-

Noob Hunter

• 2,761 posts
• Joined: 08-August 06
• Location: Oslo, Norway

Posted 22 November 2012 - 08:43

I was going through the exam slowly, working out each answer in my head... I just decided to scroll through it fully, and saw that the answers are at the end. It says:

8a2+28ab-16b2

So XerXis was correct.

#7 ozzy76

ozzy76

Neowinian

• 933 posts
• Joined: 25-November 02
• Location: USA

Posted 22 November 2012 - 08:43

FOIL (First Outside Inside Last)

this takes me back

#8 GreenMartian

GreenMartian

Neowinian Senior

• 1,778 posts
• Joined: 28-August 04

Posted 22 November 2012 - 08:44

.. its not necessary to use 'x' specifically.

Exactly. The same way that everyone knows 2b means 2xb.
a(2b) = a times 2 times b.

cell tech

• 1,436 posts
• Joined: 04-November 07

Posted 22 November 2012 - 08:55

I was going through the exam slowly, working out each answer in my head... I just decided to scroll through it fully, and saw that the answers are at the end. It says:

So XerXis was correct.

Every time I had ?'s like that in school we had to solve for each variable.... Oh well, good thing I'm not a pilot.

#10 XerXis

XerXis

Neowinian Senior

• 5,137 posts
• Joined: 13-February 06
• Location: Belgium

Posted 22 November 2012 - 08:59

Every time I had ?'s like that in school we had to solve for each variable.... Oh well, good thing I'm not a pilot.

That would be true if there was an equation, however it wasn't there. Also it's impossible to solve an equation with two variables. It wouldn't make any sense

#11 Axel

Axel

--[Est. 1986]--

• 5,456 posts
• Joined: 05-August 03
• Location: Milton Keynes, UK

Posted 22 November 2012 - 09:28

I'm a pilot and as far as I can help with that question would be to interpret it as (2a+8b)*(4a-2b). Any further than that is fairly lost on me! I don't remember my entrance exams being like that!

#12 mercenary

mercenary

Neowinian

• 31 posts
• Joined: 14-July 02

Posted 22 November 2012 - 10:08

http://www.wolframal...=(2a+8b)(4a-2b)

#13 +Nik L

Nik L

Where's my pants?

• 35,040 posts
• Joined: 14-January 03

Posted 22 November 2012 - 10:12

Why is this ridiculously simple thing being posted again?

It's been solved and debated to death less than 3 months ago.

#14 OP -Alex-

-Alex-

Noob Hunter

• 2,761 posts
• Joined: 08-August 06
• Location: Oslo, Norway

Posted 22 November 2012 - 13:06

Why is this ridiculously simple thing being posted again?

It's been solved and debated to death less than 3 months ago.

1) I didn't see the thread 3 months ago
2) Good luck searching the forums for a random equation
3) What's the big deal?

#15 +Xinok

Xinok

Resident Reresident

• 3,502 posts
• Joined: 28-May 04
• Location: Shikaka
• OS: Windows 7 x64
• Phone: Galaxy S3

Posted 22 November 2012 - 16:47