Answer:
[tex]x = 2.5[/tex]
Step-by-step explanation:
Given
[tex]AC = 2x - 1[/tex]
[tex]AB = 2x + 1[/tex]
[tex]BC = 2\sqrt{7[/tex]
[tex]\angle A = 60^{\circ}[/tex]
Required
Find x
To find x, we make use of cosine formula which states:
[tex]a^2 = b^2 + c^2 - 2bcCosA[/tex]
In this case:
[tex]BC^2 = AB^2 + AC^2 - 2*AB*BC*CosA[/tex]
Substitute values
[tex](2\sqrt{7})^2 = (2x + 1)^2 + (2x-1)^2 - 2*(2x + 1)*(2x - 1)*Cos(60^{\circ})[/tex]
Evaluate all exponents
[tex]4*7 = (4x^2 + 4x + 1)+(4x^2 - 4x + 1) - 2(4x^2 - 1)*cos(60^{\circ})[/tex]
Open brackets
[tex]28 = 4x^2 + 4x + 1+4x^2 - 4x + 1 - (8x^2 - 2)*cos(60^{\circ})[/tex]
Collect Like Terms
[tex]28 = 4x^2 +4x^2+ 4x - 4x+ 1 + 1 - (8x^2 - 2)*cos(60^{\circ})[/tex]
[tex]28 = 8x^2+ 2 - (8x^2 - 2)*cos(60^{\circ})[/tex]
Substitute 0.5 for cos(60)
[tex]28 = 8x^2+ 2 - (8x^2 - 2)*0.5[/tex]
Open bracket
[tex]28 = 8x^2+ 2 - 4x^2 + 1[/tex]
Collect Like Terms
[tex]8x^2- 4x^2 + 2 + 1 - 28 = 0[/tex]
[tex]4x^2 -25 = 0[/tex]
Collect Like Terms
[tex]4x^2 =25[/tex]
Divide both sides by 4
[tex]x^2 =\frac{25}{4}[/tex]
[tex]x^2 =6.25[/tex]
Take positive square root of both sides
[tex]x = \sqrt{6.25[/tex]
[tex]x = 2.5[/tex]
