Thread: Basic Trigonometry

The triangle ABC has sides AB [] AC [] and BC [], as well as cosBaC []

a] Write down and simplify a quadratic equation satisfied by and hence evaluate

b] Express sinBaC in the form

c] Express sinAcB in the form

I have no idea how to solve these, it's the most difficult question I have out of the exam papers and even though I (sort of) understand trigonometry at the moment this is just impossible to me.
Could anyone please help?

For a] I have a value of 8, and this I know to be right

For b] I have but I don't know how you can express it in the form asked for.

Please could someone help?

Originally Posted by db5vry

The triangle ABC has sides AB [] AC [] and BC [], as well as cosBaC []

a] Write down and simplify a quadratic equation satisfied by and hence evaluate

b] Express sinBaC in the form

c] Express sinAcB in the form

I have no idea how to solve these, it's the most difficult question I have out of the exam papers and even though I (sort of) understand trigonometry at the moment this is just impossible to me.
Could anyone please help?

For a] I have a value of 8, and this I know to be right

For b] I have but I don't know how you can express it in the form asked for.

Please could someone help?

b) you can use the formula: sin^2 A + cos^2 A =1

c) in b) you will obtain sin BaC= (square of 45)/7. you know 7cm is one side of the triangle so you know that (square of 45) cm is the height. so sin AcB=(square of 45)/9 [because 9 is the other side

Hello, db5vry!

The triangle ABC has sides: and

Code:

            B
            *
           *  *
       7  *     *   9
         *        *
        *           *
       *              *
    A *  *  *  *  *  *  * C
              x

(a) Write down and simplify a quadratic equation satisfied by and evaluate

Law of Cosines: .

We have: .

. . which simplifies to: .


Therefore: .

(b) Express in the form

Law of Sines: .

We have: .
And: .

Substitute into [1]: .

(c] Express in the form

Law of Sines: .

We have: .

Substitute into [2]: .