I need help on this question:

Q) Calculate without using a calculator the exact value of

√3 cos15 - sin15

Ans) √2

can someone show me the working of it. Thx!

(the equation isnt equal to 0 or anything)

Printable View

- Apr 29th 2009, 06:02 AMSundaetrigonometric identites
I need help on this question:

Q) Calculate without using a calculator the exact value of

√3 cos15 - sin15

Ans) √2

can someone show me the working of it. Thx!

(the equation isnt equal to 0 or anything) - Apr 29th 2009, 06:11 AMmr fantastic
Use the half angle formulas: 4. Half Angle Formulas

- Apr 29th 2009, 06:27 AMSundae
The half angle formula hasnt been introduced in the chapter yet, only the addition formula so i dont think im suppose 2 use it for this question. (and i dont know where to begin wiv tht formula).

- Apr 29th 2009, 06:31 AMmr fantastic
- Apr 29th 2009, 06:42 AMSundae
that just made things more muddled up... buh thx for ur help.

- Apr 29th 2009, 06:48 AMe^(i*pi)
What have you covered already? As far as I'm aware the two solutions proposed by Mr F are the best/only methods:

$\displaystyle cos(A \pm B) = cosAcosB \mp sinAsinB$

$\displaystyle sin (A \pm B) = sinAcosB \pm cosAsinB$

unless you're more familiar with that form.

(The half angle formulae are also derived from that form because cosA = cos(0.5A+0.5A)) - Apr 29th 2009, 07:06 AMSundae
im using the heineman c3 book, exercise 7A its only covered the additional rule.

- Apr 29th 2009, 03:40 PMmr fantastic
If you are unable to apply either of the methods I have suggested then you are currently not in a position to be able to do the question at all. In which case you will just have to wait until you have covered that material in class. Then come back and review this thread.

- Apr 30th 2009, 01:11 AMSundae
i home school >.< i dont have a teacher i been teaching myself.

- Apr 30th 2009, 02:04 AMmr fantastic
- Apr 30th 2009, 02:07 AMSundae
i understand what ur saying, i appreciate ur help. I just wanted to see the working out of the question >.<