Additional Maths - Need help with trig. equation problem

How do you re-arrange equations such as 'Cosθ=Cos65°' to find solutions for theta? I understand what to do once it's simplified to ' θ=...', but I don't know how to get to that point when Cos is on both sides of the equation

Reply 1

the bear

20

sketch the cos graph. draw a vertical line at the 65º position on the x axis. then draw a horizontal line where this meets the curve. look along the horizontal line for further intersections with the curve.

Reply 2

sena98

Original post by Tasha_140

How do you re-arrange equations such as 'Cosθ=Cos65°' to find solutions for theta? I understand what to do once it's simplified to ' θ=...', but I don't know how to get to that point when Cos is on both sides of the equation

it is answer -65 because in cosine rule, cos(-x)=cos(x)

Reply 3

username1732491

18

Original post by Tasha_140

How do you re-arrange equations such as 'Cosθ=Cos65°' to find solutions for theta? I understand what to do once it's simplified to ' θ=...', but I don't know how to get to that point when Cos is on both sides of the equation

Just find values of θ for which cosθ = cos(65°). Simples.

There are in fact infinitely many of these, however you know that a cos graph repeats every 360°, and is symmetric about the y-axis. Thus you can represent all solutions in the form 360n ± 65°, where n is an integer.

Reply 4

F3rnw3h

OP

13

Got it, wasn't thinking properly, for some reason I thought I had to re-arrange...
Yea, prefer to use the CAST diagrams to the graphs themselves as I find it a lot easier haha, but thanks! :tongue:

Additional Maths - Need help with trig. equation problem

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you