Question

sin10+sin50-sin70=?

Answer 1

Calculator?

Answer 2

no

Answer 3

by hand

Answer 4

Gt where are you?

Answer 5

Who the heck does this with hand?

Answer 6

hamidaarab

Answer 7

May be by using this silly formula then:
sin A + sin B = 2 sin ½ (A + B) cos ½ (A − B)

Answer 8

must be some trick, like writing one of them as acosine

Answer 9

And then this formula:
sin A − sin B = 2 sin ½ (A − B) cos ½ (A + B)

Answer 10

ok hamidaarab i will help u

Answer 11

just wait a second

Answer 12

This stuff is from centuries ago when they did not have calculators and needed to get the angles to add up to what the trigonometric "tables" printed in books could hold. In this modern age, it is outrageous to solve such problems, and by hand.

Answer 13

ok entourage

Answer 14

no that is wrong
\[2\sin(30)\cos(-20)\] for first term

Answer 15

That is equal to cos(-20). Then, you re-write it as sin(?). Then, use the same formula stuff with sin(70). Then, get to finally the wonderment. :)

Answer 16

guess you get zero, but i am not sure of second step

Answer 17

Isn't sin(theta) = cos(pi-theta) or something?

Answer 18

mr Gt
\[\lim \lim_{x \rightarrow \pi/4}\cos2x divsinx - cosx\]

Answer 19

2*sin(30)*cos(-20) = cos(-20) because sin(30) = 1/2.

So, you have:
cos(-20) - sin(70) to figure out. But, you can write cos(-20) as sin(-110) = -sin(20) I think.

So, you have:
-sin(20) - sin(70). Then, use the same formula again.

Answer 20

آهان فهمیدم

Answer 21

Mr GT
....=0
thank you

Answer 22

As,
=sin10+(sin50-sin70)
=sin10+[-{2cos(50+70)/2 * sin(50-70)/2}]
=sin10-{2cos60 * sin(-10)}
=sin10-{2*(1/2) * sin(-10)}
=sin10-{ sin(-10)}
=sin10+sin(10)
=2sin(10+10)/2*cos(10-10)/2
=2sin10*cos0
=2sin10

Answer 23

Now Check this out...

Answer 24

muhamman nauman umair!
i solve it!
\[\sin10+((2\sin(50-70/2)timescos(50+70/2))=\sin10+(-2\sin10\times1/2)=\sin10-\sin10=0\]