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標題:
maths (7)
發問:
1. If cos 240o – sin 2x = 0. Find x. 2. Known 2 tan 45o + sin2 x + sin2 54o = 4 – tan 45o. (a) Find x.
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最佳解答:
1. If cos 240o – sin 2x = 0. Find x. cos240 = sin2x -0.5 = sin2x 2x = 210 or 330 x = 105 or 165 2. Known 2 tan 45o + sin2 x + sin2 54o = 4 – tan 45o. 2 tan45 + (sinx)^2 + (sin54)^2 = 4 - tan45 2(1) + (sinx)^2 + (sin54)^2 = 4 - 1 (sinx)^2 + (sin54)^2 = 1 (sinx)^2 = 1 - (sin54)^2 (sinx)^2 = (cos54)^2 sinx = cos54 or -cos54 x = 36 or 144 or 216 or 306
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