C2 Trig Eqn help

Vidsify

Hi
I'm stuck on this question

ImageUploadedByStudent Room1430244841.929472.jpg

Question ci and cii

Thanks

Reply 1

aoxa

Original post by Vidsify

Hi
I'm stuck on this question

ImageUploadedByStudent Room1430244841.929472.jpg

Question ci and cii

Thanks

Use the identity sin^2 theta=(1-cos^2 theta) to get the equation all in terms of cos. Then rearrange the equation to get everything on one side (=0) and then factorise, like a normal quadratic function. Of these two values for cos theta, you should be able to eliminate one.

Use this value of cos theta to find your prinicpal value for theta and then use the graph of cosine to find the other values for theta between the values given.

Reply 2

TheMadHatteress

Sin2+cos2=1
so sin2= 1-cos2
so then it becomes a quadratic equation and you carry on like that.
for cii you do the same thing as see one except now woth 2x.
so now
cos 2 x = 3/4
amd then you find the angles normally and convert them into radians. :smile: