Math Is Fun Forum

ninjaman

Member

Registered: 2013-10-15

Posts: 61

scalene triangle

hello

I have a problem that involves a scalene triangle. I have one angle and two sides.

I know that all the angles should add to 180. so I thought with two angles I could use: 180-50-14.79= 115.21 which is the wrong answer

I have these values

A 64.783?
a 35.44

B 14.79
b 10

C 50
c 30

I know that the angle and side I have to find are correct (B and a)
though I tried the 180 thing, I got this wrong and my lecturer told me why. unfortunately I didn't write it down and cant remember what I did.

does anyone know about the 180 thing?
I have to show how I got the answers and I think the 180 thing is what I have to use but im doing it wrong.

thanks
simon:)

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: scalene triangle

Hi ninjaman

Which of those values are given to you?

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

ninjaman

Member

Registered: 2013-10-15

Posts: 61

Re: scalene triangle

b
C
c
these are given

the answers I have to find are B and a

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: scalene triangle

The angle A is incorrect. Your initial answer of 115.21 is the correct one.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

ninjaman

Member

Registered: 2013-10-15

Posts: 61

Re: scalene triangle

what would that make side a then?

I was told that the answer is gave was correct?

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: scalene triangle

Everything else is okay. All of the sides and the angles B and C.

Did your teacher tell you that 115.21 is wrong?

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,134

Re: scalene triangle

hi ninjaman,

You've got c = 30, b = 10 and C = 50

So you can use the sine rule to get B

Now to get 'a' you need

But we only know two of those so we cannot get 'a' yet.

But the angles of a triangle add up to 180.  So

So now

I have worked to 6 decimal places but rounded off here.

Bob

ps.  sin x = sin(180-x) so sin 64.79 = sin 115.21.  So you can get A wrong yet still get 'a' correct.  Be careful with this because you would lose marks if A was asked for as well.

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: scalene triangle

Hi Bob

I don't think sin(B) can be 14.79. B maybe, but not the sine.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,134

Re: scalene triangle

More gremlins.  Oh dear.  You are, once again, correct.  Would you like a job as my proof reader?

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: scalene triangle

How well does it pay?

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

Bob

Administrator

Registered: 2010-06-20

Posts: 10,134

Re: scalene triangle

Pay?  You obviously don't understand how the apprentice system works. 

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob