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c3

hi,

any ideas how to answer these questions.

ocr jan08 question 9

9) i) use identity cos(A+B)to prove
[0]

4cos(0+60)cos(0+30)= root3 - 2sin20

ii) hence find exact value82.5cos52.5

iii) solve for 0<theta<90 the equation 4cos(0+60)cos(0+30) = 1

iv) given there are no values of theta which satisfy the equation
4cos(0+60)cos(0+30) = k determine the set of values of the constant K.

cheers
well do the addition formulae to get
4(cos0cos60 - sin0sin60)
cos 60 and sin 60 have known values on ur calculator so can be multiplied with the 4 to get a constant in the form xcos0 - ysin0 then go from there using all ur identities and stufff
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