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Given that cos(x) = 1/4, what is cos(2x)?

cos(2x) = 2cos²(x) - 1 This is the identity. Therefore we can substitute in 2[cos²(x)] to be 2 multiplied by (1/4)².Therefore cos(2x) = 2(1/4)(1/4) - 1 = 2/16 - 1 = 2/16 - 16/16 =1/8 - 8/8 = -(7/8).Ans. = - 7/8.

Answered by Bhumi K. • Maths tutor

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