Mathematics

Mathematics

Problem

If 128(sin⁡8x+cos⁡8x)−97=0128(\sin^8 x + \cos^8 x) - 97 = 0 , x∈[0,2π]x \in [0, 2\pi] , then the number of values of xx is (1) 4 (2) 8 (3) 12 (4) 16
Intuitive explanation

The key is to recognize that sin⁡8x+cos⁡8x\sin^8 x + \cos^8 x can be simplified using the substitution u=sin⁡2x+cos⁡2x=1u = \sin^2 x + \cos^2 x = 1 and repeated applications of algebraic identities. By expressing higher powers in terms of sin⁡2xcos⁡2x\sin^2 x \cos^2 x, you'll reduce the equation to a polynomial in a single variable. Once you solve for that variable, you'll find the corresponding values of xx in the given interval by carefully counting solutions to basic trigonometric equations.

Intuitive explanation

The key is to recognize that sin⁡8x+cos⁡8x\sin^8 x + \cos^8 x can be simplified using the substitution u=sin⁡2x+cos⁡2x=1u = \sin^2 x + \cos^2 x = 1 and repeated applications of algebraic identities. By expressing higher powers in terms of sin⁡2xcos⁡2x\sin^2 x \cos^2 x, you'll reduce the equation to a polynomial in a single variable. Once you solve for that variable, you'll find the corresponding values of xx in the given interval by carefully counting solutions to basic trigonometric equations.

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