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Solve the equation cos2x - 5cosx = 2

cos2x= 2cos^2x - 1

2cos^2x - 1 - 5cosx = 2

Let cosx = y

2y^2 - 5y - 3 = 0

(2y + 1)(y + 3) = 0

y = -1/2 or -3

cosx = -1/2 or -3

x = 120 degrees

Answered by Pearl V. • Maths tutor

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Expand the expression (1+3x)^1/3 up to the term x^3.

= 1 + 3x1/3 + (1/3-2/3)(3x)^2 + (1/3*-2/3*-5/3)(3x)^3

= 1 + x - 2x^2 + 10x^3

Answered by Pearl V. • Maths tutor

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5664 Views