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Geometry Level 2

what is the value of x ?


The answer is 1.

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1 solution

(x+5)/sin⁡(2θ) =(x+3)/sin⁡(θ) =(x+4)/sin⁡(180-3θ)

(x+5)/(2 sin⁡〖(θ) cos⁡(θ) 〗 )=(x+3)/sin⁡(θ)

cos⁡θ=(x+5)/2(x+3)

sin⁡(180-3θ)=sin⁡(3θ)

sin⁡(3θ)=sin⁡(2θ+θ)=sin⁡(2θ) cos⁡(θ)+cos⁡〖(2θ) sin⁡(θ) 〗

2 sin⁡(θ) cos^2⁡(θ)+=sin(θ) cos⁡(2θ)

〖=sin〗⁡(θ)[cos⁡(2θ)+〖2cos〗^2⁡(θ) ]

〖=sin〗⁡(θ)[2 cos^2⁡θ-1+2 cos^2⁡(θ) ]

〖sin⁡(3θ)=sin〗⁡(θ)[4 cos^2⁡θ-1]

4 cos^2⁡θ-1=(2 cos⁡(θ)-1)(2 cos⁡(θ)+1)

(x+3)/sin⁡(θ) =(x+4)/sin⁡(3θ)

(x+3)/sin⁡(θ) =(x+4)/sin⁡(3θ)

(x+3)/sin⁡(θ) =(x+4)/sin⁡(3θ)

(x+3)/sin⁡(θ) =(x+4)/(sin⁡(θ) [4 cos^2⁡θ-1])

4 cos^2⁡θ-1=(x+4)/(x+3) (2 cos⁡(θ)-1)(2 cos⁡(θ)+1)=(x+4)/(x+3)

[(2) (x+5)/2(x+3) -(x+3)/(x+3)][(2) (x+5)/2(x+3) +(x+3)/(x+3)]

[2/((x+3) )][(2x+8)/((x+3) )]=(x+4)/(x+3)

[(4(x+4))/(x+3)^2 ]=(x+4)/(x+3)

[4/((x+3) )]=1/1

4=x+3 x=1

You first make use of the sine law. then equate it so that one side is sec (theta) which is (2x+6)/(x+5). Then use cosine law. Expanding it and arriving to an equation where one side is sec(theta)=(2x^2+18x+40)/(x^2+12x+32). Substituting the first equation and simplifying it arrives in 2x^2+6x-8=0. Solving for x yields 1 and -4. That makes x=1.

Amiel Clark Casidsid - 7 years, 2 months ago

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thanks for you

Mohammed El-Ghobary - 7 years, 2 months ago

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