Ashley Yeo Sze Lin's answer to lana <3's Secondary 3 A Maths Singapore question.
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For part 1, use the trigo identities to derive the answer
For part 2, sub in the answer from part one and do not divide, as the solution will not make sense (you would get 1 = sqrt(2))
For part 2, sub in the answer from part one and do not divide, as the solution will not make sense (you would get 1 = sqrt(2))
Date Posted:
2 years ago
hi! how to you get theta - 70 = 90 or 270 ?? how do yk its 90 or 270
so to get a solution, cos (theta - 70) must be zero. only cos 90 and cos 270 are equal to 0 in the given range
oh I think I understand! so if sin(theta+20) = 0 the range would be 180 < theta < 360
so the way i understood the concept was that the cos value corresponds to the x value of the angle drawn. since theta is between 0 and 360, theta -70 is between -70 and 290. i used cos for this qtn
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