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how to work out sin4x = 1/2

how do you work out sin4x = 1/2

Reply 1

sin (2x + 2x) = 1/2 ?

then expand, to get sin2xcos2x + cos2xsin2x

Reply 2

arcsine both sides...

4x = pi/6, 5pi/6, 13pi/6, 17pi/6...

dum dum dum.

Reply 3

snob_uk

sin (2x + 2x) = 1/2 ?

then expand, to get sin2xcos2x + cos2xsin2x

uh, how does that help?

Reply 4

I don't think it does help :s-smilie:

:s-smilie:

Reply 5

probably just got trig identities on the brain. mustve had c3 today. :biggrin:

:biggrin:

Reply 6

OP

snob_uk

sin (2x + 2x) = 1/2 ?

then expand, to get sin2xcos2x + cos2xsin2x

I did all that but i can't get to the right answer........can anybody show me?

Reply 7

Is there a range?

Reply 8

snob_uk

sin (2x + 2x) = 1/2 ?

then expand, to get sin2xcos2x + cos2xsin2x

I think you are making it more difficult than it looks

Reply 9

OP

mizfissy815

Is there a range?

Between 0 and 180 degrees

Reply 10

sin4x = 0.5
sinØ =0.5 ........0«Ø« 720
Ø= 30,150, 390, 510

4x= 30/150/390/510
x= 7.5/ 37.5/ 97.5/ 127.5

Reply 11

chewwy

arcsine both sides...

4x = pi/6, 5pi/6, 13pi/6, 17pi/6...

dum dum dum.

methinks chewwy knows how to do this.

You should get lots of answers.

Sin-1 1/2 gives 30 degrees.

Use the cast diagram to tell you the regions where sin is positive.

find ur answers from 0 to 720 degrees (4x = 4 x 180)

Divide by 4

Reply 12

I like these questions because they give away so many easy marks in C2 exams. One P1 paper gave 8 marks. Nice.

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