Urgent! Trig: The Area formula!

G

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Ok so the question asks:
Find the marked angle in the following triangles in degrees, minutes and seconds.
So there's a picture of a triangle,
one side is 51m long,
another is 75m long
nd you get the area which = 1683m^2
and you have to work out the angle between the two sides your given using...
Area=1/2bcsinA

This is what I've got so far...
Area=1/2bcsinA
1683=1/2x51x75xsinA
sinA=1683
1/2x51x75
So the answer I got was sinA=0 degrees 52'48"
but that's not the right answer.

Some how I have to get to...
61 degrees 39' or 118 degree s21' as my answer
but I don't know how!
Possibly you could tell me how to put it into my calculator for future referance my half yearly is on Tuesday!

Thanks alot if you can help me I streesing soo bad!
 
(1/2)*51*75*sin(A) = 1683
51*75*sin(A) = 2*1683
sin(A) = (2*1683)/(51*75)

A = arcsin[(2*1683)/(51*75)] = 61.64236342 = 61 deg 38 min 32.508 sec

A = 180 - arcsin[(2*1683)/(51*75)] = 118.3576366 = 118 deg 21 min 27.492 sec
 
Re: Help!

Alicia said:
I have no idea what your talking about!

... then you best do some research on the inverse sine function and how it works with a calculator.
 
Reply

Its just you've done it completely different to how the book says to do it!
The book says...
Find the value for A in the triangle shown, assuming that the area of the triangle is 31cm^2. Answer in degrees and minutes.
As an example

1. Write the formula.
Area=1/2bcsinA

2. Give the values of the area, b and c.
Area=31cm^2, b=12cm, c=8cm

3. Substitute these values into the equation.
31=1/2x12x8xsin A

4. Rearrange for A. sin A= 31 over 1/2x12x8

5. Solve for A, listing both possibilities
A= 40 deg. 14 min. or 180 deg. - 40 deg. 14 min.
A= 40 deg. 14 min. or 139 deg. 46 min.

I just don't know how they got from step 4 to step 5
ok...
I have a Sharp EL-531VH Advanced D.A.L. scientific calculator
all I want to know is which buttons to push, this is what I did...
31 [divide by button] (1/2 [x] 12 [x] 8)
which = 0 deg. 38 min. 45 sec.
which is obviously wrong.

PS what does * mean????? and y'd you move the two to the otherside?????
 
Alicia said:
Its just you've done it completely different to how the book says to do it!
The tutor provided a fairly standard methodology. If you are supposed to use something other than inverse trig functions, please say so.

Alicia said:
I have a Sharp EL-531VH Advanced D.A.L. scientific calculator
all I want to know is which buttons to push...
Then please read your owner's manual, which should have step-by-step instructions.

Alicia said:
PS what does * mean?
This multiplication symbol indicates "times". For further information on textual formatting, please follow the link to "Karl's Notes" in the "Forum Help" pull-down menu at the very top of this page.

Alicia said:
and y'd you move the two to the otherside?
I'm sorry, but I do not understand what "y'd" means. When you reply, please also clarify who "you" is, which "two" whats were moved, and "to the otherside(sic)" of what.

Thank you.

Eliz.
 
Alicia said:
Area=1/2bcsinA
1683=1/2x51x75xsinA
sinA=1683
1/2x51x75
So the answer I got was sinA=0 degrees 52'48"
but that's not the right answer.
Well, we sure have no idea what YOU're talking about...

What does 1683 / (1/2 * 51 * 75) equal? : in future, use * for multiplication, not "x"

Once you get that, it becomes the SINE of the angle: what is that angle?

By the way, 1683 / (1/2 * 51 * 75)
= 1683 / (51 * 75 / 2)
= 1683 * 2 / (51 * 75) : that's WHY the "2" moved!
If you can't follow that, you're SURE not ready for angles and SINE of angles...
 
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