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# FSMQ Additional Maths help watch

1. Hi, I' doing an additional maths past paper and don't know how to do this five mark question:
Solve the equation 5sin2x=2cos2x in the interval 0<x<360

(the more than and less than signs should be including 0 and 360)
Thank you!
2. (Original post by xxjessietxx)
Hi, I' doing an additional maths past paper and don't know how to do this five mark question:
Solve the equation 5sin2x=2cos2x in the interval 0<x<360

(the more than and less than signs should be including 0 and 360)
Thank you!
so you know the trigonometric identity : sinx / cosx = tanx ?

use this:

divide both sides by cos2x

so 5sin2x/cos2x = 2cos2x/cos2x
5tan2x = 2
tan2x = 0.4
2x = tan^-1(0.4)
= 21.8 , 201.8, 381.8, 561.8(, 741.8) (degrees)
(because it's 2x, limit is now 720 degrees)
x = 10.9, 100.9, 190.9, 280.9(, 370.9)
because range is from 0-360 degrees, x = 10.9, 100.9, 190.9, 280.9 (degrees)

hope that helps
3. Thank you that makes sense now xxx
4. (Original post by xxjessietxx)
Thank you that makes sense now xxx
No worries How long have you been learning the content for Additional Maths?
5. I started last year but we only have one lesson a week and there's only four of us doing it

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