a) Given x is obtuse and sin x = 5/13, find the value of cos 2x b) Show that secx - cosx ≡ tanxsinx
Need help on both of them
What have you done?
A tip for the first one: Think about Pythagorean Triples. Do those numbers ring a bell? Then note that x is obtuse, so is cos x positive or negative? Once you know sin x and cos x you can find cos2x.
For questions like the second one, if in doubt, write the everything solely in terms of sin then cos, then experiment with multiplying through with things.
A tip for the first one: Think about Pythagorean Triples. Do those numbers ring a bell? Then note that x is obtuse, so is cos x positive or negative? Once you know sin x and cos x you can find cos2x.
For questions like the second one, if in doubt, write the everything solely in terms of sin then cos, then experiment with multiplying through with things.
For part a) I drew out a triangle to work out that cosx = -12/13. Is this what you got?
a) Given x is obtuse and sin x = 5/13, find the value of cos 2x b) Show that secx - cosx ≡ tanxsinx
Need help on both of them
For part 1 use the formula sinx=root ((1-cos2x)/2) For part 2 since secx is 1/cosx substitute it there then add, you should get sin^2x/cosx after placing sin^2x in place of 1-cos^2x. then split. that's it
You need to somehow turn two terms (the left-hand-side) into one term and normally the best way to do this is to combine fractions.
So you can write sec(x) = 1/cos(x) and then subtract the fractions i.e. put them over a common denominator. Try this and post your working if you get stuck.
yes. That's right. Alternatively you could have used sin^2 x + cos^2 x = 1.
thank you everyone i just figured out both the questions. I feel so dumb rn i dunno how i didn't see it before. :d thanks for all your help, reps for you all xxx