6 sin 112,5 sin 22,5 = .....
teach me please

Question

6 sin 112,5 sin 22,5 = .....
teach me please

ganeshie8 · Answer

hint : 
112.5 = 180 - 67.5
22.5  = 90 - 67.5

anonymous · Answer

but these is "6sin" how?

ganeshie8 · Answer

$\large   6~ \sin (112.5) ~~ \sin (22.5)  $

ganeshie8 · Answer

$\large   6~ \sin (180 - 67.5) ~~ \sin (90-67.5)  $

ganeshie8 · Answer

can u take it from here ? :)

anonymous · Answer

i'm confuse. in my book the formula is 2sinAsinB=cos(A-B)-cos(A+B). and i really confuse :(

ganeshie8 · Answer

oh yes, thats a very nice formula.
lets use that :)

ganeshie8 · Answer

$\large   6~ \sin (112.5) ~~ \sin (22.5) $

$\large   3 \times 2 ~ \sin (112.5) ~~ \sin (22.5) $

ganeshie8 · Answer

u can apply the formula now ?

ganeshie8 · Answer

$\large   6~ \sin (112.5) ~~ \sin (22.5) $

$\large   3 \times 2 ~ \sin (112.5) ~~ \sin (22.5) $

$\large   3 \times [\cos  (112.5 - 22.5) - \cos(112.5 + 22.5)] $

anonymous · Answer

3 x (cos90-cos 135)
3 x (0-cos135)?
3x -cos 135?

ganeshie8 · Answer

Yes !

ganeshie8 · Answer

whats cos(135) ?

anonymous · Answer

i dont know haha

ganeshie8 · Answer

-3 cos (135)

-3 cos ( 90 + 45)

use cos (A + B) formula :)

ganeshie8 · Answer

cos(A + B) = cosA cosB - sinA sin B

ganeshie8 · Answer

-3 cos ( 90 + 45)

-3 [cos90 cos45 - sin90 sin 45]

-3 [0  - 1/sqrt(2)]

3/sqrt(2)

anonymous · Answer

oke thak ou very much :)

ganeshie8 · Answer

np :)

anonymous · Answer

you're so helpful :)

anonymous · Answer

can i ask once more?

ganeshie8 · Answer

sure ask...

anonymous · Answer

If θ is in quadrant 1 and tan θ = 5/12. The value of tan 4θ/5 = ...

ganeshie8 · Answer

not use if there is any smart way, il try like below :- tan θ = 5/12 => θ = arctan(5/12) = 22.62 degrees http://www.wolframalpha.com/input/?i=arctan%285%2F12%29+degrees%29

ganeshie8 · Answer

tan(4 θ/5) = tan(4 * 22.62/5) = 0.327 http://www.wolframalpha.com/input/?i=tan%284+*+22.62%2F5%29

anonymous · Answer

thank ypu ::)