# An algebra question I can't figure out

#### Corey Esson

Joined Feb 8, 2015
30
Okay, one more question I'm just not understanding.
40 ∠40° x 30 ∠20° equals?

A. 70 ∠80°
B. .75 ∠60°
C. 1200 ∠60°
D. 70 ∠800°

I personally have no idea what this could be? Not even any suggestions.
Any and all suggestions are appreciated.
Thank you,
Corey

#### shteii01

Joined Feb 19, 2010
4,644
Could be vector multiplication.

#### Corey Esson

Joined Feb 8, 2015
30
Could be vector multiplication.
Just can't figure out how to key it into my calculator?

#### WBahn

Joined Mar 31, 2012
26,271
Just can't figure out how to key it into my calculator?
Do you know how to do it by hand?

If you understand how to multiply two vectors, then the answer is obvious by inspection.

If your understanding of these concepts is limited to memorizing what buttons to push on a calculator, then you are crippling yourself big time.

So set the calculator aside and do it by hand. If you don't know how to do it by hand, then that is what you need to focus on.

#### shteii01

Joined Feb 19, 2010
4,644
Just can't figure out how to key it into my calculator?
You will have to change the notation.

#### Corey Esson

Joined Feb 8, 2015
30
Do you know how to do it by hand?

If you understand how to multiply two vectors, then the answer is obvious by inspection.

If your understanding of these concepts is limited to memorizing what buttons to push on a calculator, then you are crippling yourself big time.

So set the calculator aside and do it by hand. If you don't know how to do it by hand, then that is what you need to focus on.
Shteii01 and Wbahn, thank you very much. No, I don't know how to do it by hand as I'm algebra stupid, lol! But I did figure out how to do it by hand and then by calculations. Answer is C. 1200∠60°.
Yes I am going to have a heck of a time here.
Again, thank you to both!!
Corey

#### WBahn

Joined Mar 31, 2012
26,271
Shteii01 and Wbahn, thank you very much. No, I don't know how to do it by hand as I'm algebra stupid, lol! But I did figure out how to do it by hand and then by calculations. Answer is C. 1200∠60°.
Yes I am going to have a heck of a time here.
Again, thank you to both!!
Corey
Being "algebra stupid" is nothing to proud of -- it is crippling you. Consider if this were a test and how much time you just spent trying to get this one answer -- time which would now be unavailable to spend on all of the other questions. Yet if you understand how to multiply two vectors you know that the answer has to have an angle that is the sum of the angles of the two factors. Assuming that you can add 20 and 40 to get 60 (not trying to be snide, I've just seen too many people whose math skills are sufficiently weak that they can't do that without a calculator and that who have been proud of that fact since it proves that they "don't waste time memorizing useless facts"), then you know immediately that the answer must be either B or C. That alone gives you a 50/50 chance even if you guess from there. But now consider the product of 40 and 30. Can it possibly be 0.75? If not, then the answer must be C. Got it done in less time than it would take you to pick up your calculator!

#### Corey Esson

Joined Feb 8, 2015
30
Thank you. No I'm not proud of it, just kicking myself for not taking it in high school. Here I am at 46 and sure wishing I'd done it. Now, going to bone up on algebra by hand and learn it proficiently.
Again, thank you.

#### WBahn

Joined Mar 31, 2012
26,271
Thank you. No I'm not proud of it, just kicking myself for not taking it in high school. Here I am at 46 and sure wishing I'd done it. Now, going to bone up on algebra by hand and learn it proficiently.
Again, thank you.
MUCH better attitude! Yep, you've got some catch up to do, but the time and effort will be well spent. Good luck!

#### crutschow

Joined Mar 14, 2008
25,632
You also need to study some basic trigonometry, since the problem you needed to solve is basically trig.